THE EFFECT OF HIGH TEMPERATURES ON THE GERMINATION AND SUBSEQUENT GROWTH OF CORN BY AARON RAYMOND KIENHOLZ B.S. North-Western College, 1917 M.S. University of Illinois, 1920 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN BOTANY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS, 1922 URBANA, ILLINOIS UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL May 12 _, 192 . 2 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY _ Aaron R aymond KienhoJLz ENTITLED The Ef f. eat of Hi gh Temperatures on the _ Germination and Sub s equ ent Growth of Corn BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of P hiloso phy in Botany Recommendation concurred in* $ si LO, Committee on Final Examination* •Required for doctor’s degree but not for master’s 489049 Digitized by the Internet Archive in 2016 https://archive.org/details/effectofhightempOOkien TABLE OF CONTENTS I. INTRODUCTION 1 1. Acknowledgment 5 II. MATERIALS 6 1. Description of corn used. 2. Selection of corn. III. METHODS .17 1. Apparatus used. 2. Mixtures to secure temperatures. 3. Treatment of corn after heating. 4. Methods used in heating. IV. RESULTS AND DISCUSSION 27 1. Heating of air-dry corn at 100°, 90° , 80° and 70°C 27 2. Desiccation over sulphuric acid 33 3. Moisture determinations ..43 4. Gradient of Desiccation 48 5. Daily Variation 52 6. Placing in water after heating 56 7. Growth in soil, of heated corn 58 V. CONCLUSIONS 62 VI. LITERATURE CITED 64 VII. VITA 66 i - 1 - I. INTRODUCTION. There has been a considerable increase in the use of heat in the disinfection of cereals against both insect and fungous pests, with- in recent years. Several publications have been issued with a view to disseminating knowledge among farmers, seedsmen and millowners, for the control of insects affecting stored grains and mill products. These publications are of value for that purpose, but the investiga- tions upon which they are based too often neglect phases of the sub- ject which are of intense interest to the plant physiologist from a scientific point of view and to the farmer and seedsman from a practical point of view. The investigators have too often been en- tomologists interested only in the destruction of the insect pests, or heating and ventilating engineers, with the same end in view. They have paid some attention to the effect of the heat upon the edibility and keeping qualities of the grain but have seldom paid the amount of attention, that the subject deserves, to the effect of sterilizing measures on the viability of the grain. They have not worked with carefully controlled temperatures or periocfc of exposure and seldom give details as to the moisture content of the seed, the method of heating or the variety, or even the kind of seed used. Furthermore, detailed and careful experiments are seldom carried out to determine the percent of germination after the treatment. This kind of investigation is often useless to the botanist seek- ing for definite information, but more important,, it is sometimes positively harmful to farmers and seedsmen, who, acting on the in- formation given, treat their seed, only to find the germination lowered or the seed killed outright. Goodwin (1922) makes this < . , . . ( < - 2 - statement in an Ohio Experiment Station publication, "Corn heated to a temperature of 140°F (60°C) for almost 2 days germinated almost as well as an untreated sample from the same lot”. But adds, “Of course there is the possibility that damp seed might be injured by being raised too rapidly to such temperatures as here recorded”. Although I did not heat corn at 60°C , I did, however, get severe injury after heating corn at 70°C for 140 minutes, germination being reduced from about 98 percent to 40 percent. The corn I used contained about 10.5 percent moisture, which is lower than the moisture content of most air-dry corn. Similarly, de Ong (1919) working with various seeds, including corn, gives heat treatments of 100°- 158°F for 5 hours, 124°-154°F for 2 hours, and 125 °F for 8 hours and gets an average germination percent of 86 percent, 88 percent and 94 percent respect- ively. He says the effect on grains is so small as to be almost negligible. Corn is included among the grains, though it is much more sensitive to heat than wheat and barley, and would be injured by heat which would not affect these grains. The artificial drying of cereals or other seeds to prevent loss in storage should likewise be carried on under carefully controlled conditions and at temperatures known to be low enough not to injure the viability of the corn at a given moisture content. This is es- pecially important in the drying of corn to be used for seed, during seasons when frost necessitates an early harvesting of the crop, while it is full of moisture and liable to “heat" in storage, unless dried. Insufficient data is available on the moisture-temperature relations of most of our cereal seeds and one of the purposes of this investigation was to determine the temperature relations of air-dry ahd desiccated corn. , ■ . With the failure to control certain seed borne diseases by means of chemical disinfectants, lias come the attempt to control them, first by hot water treatments, then dry heat treatments, and finally heat following soaking treatments. Here again we find insufficient atten- tion paid to the effect of these treatments on the germination, and above all, on the subsequent growth and yield of the plants from treated seed. Many seed borne diseases, especially those where the fungus is within the seed itself, are being studied and an attempt made to control them by dry heat. Atanasoff and Johnson (1920) have reviewed the earlier work on the use of dry heat in the control of disease, preparatory to a discussion of their own results on the con- trol of various cereal diseases borne on the seeds of wheat, barley, rye and oats. They heated these seeds in a gas or electric oven at 100°C for 15 and 30 hours* They state that the germination, in sand, was lowered slightly compared with untreated checks, and that the plants from treated seed were slow to start but soon caught up with their checks and remained normal. They make no mention of the kind of container in which the seed was heated, whether the seed was spread out in a thin layer or heaped together in a smaller container, nor do they mention moisture content beyond saying, ’’good dry seed of barley, wheat, oats and rye is able to withstand suprisingly well the high temperature used, up to 30 hours "y These results should by no means be interpreted as being applicable to corn and before this method of seed treatment is broad casted among farmers or seedsmen, additional work should be done, to determine what is meant by "good dry seed" and how frequently it exists in the farmer’s bins under ordinary storage conditions* Dickson (1920) working at the same station as Atanasoff and Johnson (1920) later recommends 3 hours -4- exposure to 100°C as a control measure against wheat scab and seed- ling blight of wheat, but says nothing further concerning methods. Walker (1922) has attempted to control cabbage-black leg by means of dry heat treatment of the seed. He has made moisture determinations of the seed treated. With the increasing importance of root and stalk rots of corn in the United States, comes the attempt to control or lessen its damage Soil treatments have proved unreliable, and seed treatments have proved unsatisfactory, although Branstetter (1922) reports a lessen- ing in the number of diseased plants from seed treated by immersion in alcohol and mercuric chloride, as compared with untreated checks. The possibility of heat treatment presents itself, but before this is attempted we should know something of the temperature relations of the corn to be treated. To determine the time -temperature relations of corn with known amounts of moisture, especially in the air-dry condition; to deter- mine the effect of desiccation on viability and resistance to heat, and to note the effect of heat treatment of the seed on the subse- quent growth of the seedling, are the facts to be established in this investigation. Three types of corn, varying in amount of infection and suscepti- bility to disease under field conditions, and varying in physical composition, were used in determining the above facts, and any varia- tion in response to the conditions imposed by the experiment, was noted, in the hope of being able to explain this variation by means of the characteristics of the different kinds of corn used. Thus de- termining the characters w r hich govern the behavior of corn in re- sponse to various factors, such as temperature and humidity. g . . . . , . ' . , ACKNOWLEDGMENT The work upon which this thesis is based was done in the Laboratory of Plant Physiology under the direction of Prof. Chas . E. Hottes and the writer gratefully acknowledges his help in the selection of the problem, in its development, and in the presentation of the results. . - 6 - II. MATERIALS. Three types of corn were used in this investigation. These three types varied as to their physical characters, vitality and degree of infection with various root-rot fungi. All three types were of the Reid's Yellow Dent variety, were from the 1920 harvest and were fur- nished by Mr. J. R. Ho lb ert, plant pathologist in the U. S. Depart- ment of Agriculture, of Bloomington, 111. According to results ob- tained on the germinator, Mr. Holbert classified them as: (1) Ap- parently diseased; (2) Original composite (badly diseased) and, (3) Apparently disease-free. Throughout this investigation these types of corn will be known as: (l) Peoria County Bad (PCB) , (2) Pox (Fox) and, (3) Peoria County Good (PCG) respectively. Each of these three types he further classified according to; (1) physical characters, (2) vitality, and, (3) degree of infection. The physical characters of these types of corn are of interest because of the correlation known to exist between them and resist- ance or susceptibility to root-rots. They are classified as; (l) physical composition of kernels, (2) indentation of kernels, (3) brightness of shanks, (4) brightness of kernels, (5) development of kernels, (6) tip covering of ears and (7) lustre of ears. Of these; physical composition, indentation, brightness and development of the kernels, come under direct consid- eration in this investigation. These characters, expressed in per- centages are summarized in Table I. • t : . < : - , t . . , « « < , , ' : . Cabla I. iPhysical Characters of Gom Figure 3. Rough ears of Fox. - 10 - - 11 - Figure 4. Smooth, medium and rough ears of PCG , PCB and Fox. - 12 - From this table it is noted that PCG corn possesses, to a high de- gree, many of the physical characters which are correlated with slightly infected, resistant corn. Thus; it has a high percent of horny, smooth, bright, plump kernels; good lustre of ears, and ears with tips covered. PCB corn has a few of the characters correlated with infected, susceptible corn, such as; dull, shriveled kernels and dull lustre of ears. More important, however, is its large per- cent of starchy kernels. My results indicate that this character is correlated with its ability to take up and give off moisture and largely determines its subsequent behavior. Pox, on the other hand, has many of the characters common to badly diseased corn, such as; a high percent of rough, medium bright and medium starchy kernels; and medium lustre of ears. Its high percent of medium starchy ker- nels accounts for its behavior in regard to moisture content. My own observations on the ears used in this study, coincide with those of Mr. Holbert, made on the entire lot from which the ears which I used were taken. Figures 1, 2 and 3 indicate the smooth ears of PCG; the medium ears of PCB, and the rough ears of Fox, while these may be more easily compared in Figure 4. After germinating 30 kernels from each ear, noting its percent of germination, the degree and kind of infection on the germinator, Mr. Holbert classified each of the types according to vitality and degree of infection. - 13 - TABLE II. VITALITY AND DEGREE OE INFECTION. Type of corn Vitality Degree of Infection Fusarium Diplodia PCB 99.48 3.45 Fox 96.5 12.7 1.5 PCG 99.4 0.9 ..... It is not to "be thought that because the words rt Bad M and "Good" are used in designating two of the types of corn, the vitality of the former is low. These terms refer to relative susceptibility to disease under field conditions. Mr. Holbert’s tests show PCB to have a slightly higher percent of germination than PCG, while my tests, (PCB-96.8^; Fox-93. 2% PCG-97.4^) on the corn used, show PCB to have a lower percent of germination than PCG. My tests show a lower percent throughout, probably due to greater age of the corn and less ideal growth conditions obtaining in the rag doll. Tables I and II were constructed from unpublished data kindly furnished by Mr. Holbert, to whom thanks are due. The corn was received at the laboratory on the ear and was stored in a dry place in large covered tin boxes. In the early work individual ears of each type were used as the source of the corn tested, record being kept of the number of the ear, and all of the good kernels from the ear, except those at the extreme tip and butt, being used. It was soon noticed that individual ears varied widely in their resistance to heat, their vigor of germina- tion and their degree of infection. In order to arrive at the ex- tent of this variation, 6 ears of each type were taken at random and were tested at 80° and 90°C. The results of these tests are summarized in Table III -14- Tabla III , — Individua l Variatio n of t he Ears — Stannary . Peoria Gounty Bad, Fox Peoria County G-ood o u . o © u First trial 2nd trial ■Cl© I CD O o 90 u Aver- age © Ih •§a I 30° 90° Aver- age g* CO o o 90 J 80° 90° Aver- age 70 t. r r OU» u 50.0 58.3 12 57.5 32.0 44.8 17 30.0 50.0 16.7 40.0 34.2 72 86.7 47.5 67.1 28 62.5 12.0 37.3 18 40.0 50.0 20.0 33.3 35.8 116 80.0 50.0 65.0 37 62.5 36.0 49.3 33 57.5 57 1 5 43.3 40.0 49.6 lb 7 86.7 47.5 67.1 38 55.0 36.0 45.5 54 37.5 57.5 23 . 5 45.3 40.4 166 91.7 50.0 70.9 55 55. 0 40.0 47.5 80 55.0 52.5 43.3 43.3 43.5 176 76.6 SO. Q 68.3 75 67.5 40.0 53.8 93 55. Q 37.5 20.0 30,0 50.5 70 ,58.* 8 78.3 88.6 12 38.4 93.0 65.7 17 61.3 65.8 9.7 74.3 52.8 72 96.0 86.5 91.3 28 MiA 78.3 62.6 18 46.5 68.3 5.7 85.7 51.6 116 90.5 122.0 110.3 37 30.6 121.3 76.0 33 51.5 34.5 21.7 61.3 54.8 lb? 88.5 66.0 77.3 38 37.4 92.8 65.1 54 30.5 41.0 22.7 40.3 38.6 166 89.0 65.3 77.2 55 37.0 89.8 63.4 80 73.3 72.0 11.3 99.7 64. 1 176 85.2 77.3 81.3 75 40.8 79.8 60.3 93 37.8 62.5 5.7 70.3 44.1 © c5 o © ► -15- Some ears did not vary widely from the average, or were not con- sistent in their variation, while others; notably, Fox #75 and PCG #33 were consistently high in percent of germination and length of plumule, and still others; as PCG #93 were lew in percent of germina- tion and length of plumule. The corn kernels often had their coats broken, especially was this true of the rougher ears such as those of Fox, where the shriveled, attenuated crown, which caused the roughness of the ears, is very easily broken. These kernels were discarded, as were also those in- jured by the grain moth. Some kernels had their tips broken off, exposing the black cap covering the lower part of the embryo. To de- termine whether these kernels were more readily injured by heat than those with the tips intact tests were made, using the three types of corn. The tips were in most cases, broken off artificially, but differed ih no way from those whose tips were broken off in the shell- ing process. Kernels with tips broken off gave 39.3 percent germination, while kernels with tips intact gave 44.7 percent germination, a difference of 5.4 percent. There was practically no difference in length of plumule. Each type responded similarly to this treatment. No tests were made of kernels with their crowns broken, though results would probably have been less significant than those given above. This difference justified me in selecting onl}' - kernels with tips intact. Because of the variation between individual ears, most of the in- vestigation was carried on with composite samples obtained by select- ing the same number of good kernels from each ear and mixing them thoroughly. This composite was kept in tin cans in the laboratory. By selecting 50 kernels from each ear, and having 63 ears of PCB , 33 ears of Fox, and 45 ears of PCG to select from, enough corn of , < . . , , , . . . . < , -16- a fairly composite nature was obtained for a period of work, and this was repeated as more corn was needed. These investigations involve the use of 30,000 kernels, tested in lots of 10 and 25, unless otherwise indicated. . „ -17- III. METHODS . The apparatus used in the heating of the seeds was similar to that used by Groves and described by him in the Transactions of the 111. Academy of Science 8:133-136, 1915, It consisted of two copper baths 15.5 cm. high, 21 cm. in diameter with a capacity of about 4 liters. (Fig . 5) The top was perforated by 10 tubulatures, 3 cm. in diameter, around the periphery and one in the middle. These baths were placed on electric hot plates. They were exactly the size of the hot plate and a galvanized iron sleeve was fitted around the base of the bath, extending down over the hot plate thus preventing rapid radiation of heat and at the same time holding the bath in place. In the center tubulature of each boiler a double bulb reflux condenser made of block tin was tightly fitted. The temperature of the bath was measured by a standard, go vernment- tested , Centigrade thermometer which could be slipped in and out of a glass tube leading down into one of the glass phials described below. One of these thermometers was fitted into a tubulature in each boiler. These phials contained corn to keep the bulb of the thermometer from having direct contact with the glass. This left 9 tubulatures which could be used for the heating of the corn. The glass phials were 9 cm. x 2 cm. and were fitted with rubber stoppers thru which extended 6 inch capillary tubes of 1 ram. bore. These capillary tubes were used to allow for the escape of the ex- panding , heating air and thus hasten a rapid adjustment of tempera- ture. Several tests were made to determine whether a difference in the size of the opening leading down into the phial resulted in a difference in the percent of germination. A series, using the cap- illary glass tubes, with openings 1 mm. in diameter, was contrasted with one using the ordinary glass tubes with openings 4 mm. in - — — — ♦ t • ■ t < • * < • < . . . < - . ( - 18 - Figure 5. Apparatus used in heating. diameter. The average percents of germination of three trials at 80° and 90°C were 10.6 percent and .3 percent in favor of the ordina- ry glass tubes and 4.0 percent in favor of the capillary tubes. The plumule lengths vary slightly in the same way. These results would indicate that this slight difference in size of openings has little, if any, effect on the resistance of the treated corn to heat, A larger rubber stopper at the upper end of the capillary tube, fitted the tubulatures in the copper bath and supported the phial in the liquid. (Fig. 5) By adjusting the distance between the two stoppers, the phials were, in all cases, completely submerged, in order to make the temperature of the phials uniform throughout and also to make visible any leakage which might occur around the stoppers. If' any leakage did occur the test v/as of course discarded. When not in use the tubulatures in the boiler v/ere kept tightly closed with corks in order to reduce to a minimum the loss from evaporation and the con 1 sequent change in the boiling point of the fluid. To obtain the temperatures desired, advantage was taken of the dif- ferent boiling points of various liquids and various mixtures. Thus; to secure a temperature of 100° a mixture of glycerine and water was used in the proportion of 13$ glycerine to 87$ water. This mixture boiled at exactly 100°C and the condenser refluxed the liquid back into the boiler, thus maintaining a uniform temperature. To secure j temperatures of 90°C and 80°C, mixtures of ethyl alcohol and water were used, while to secure a temperature of 70°C a mixture of methyl alcohol and water was used. The exact proportions of the mixtures used are summarized below: ■ " , , . . . * . , • * - 20 - Temperature Distilled Water 100° c 87 $ - g lycerine - 13$ 90°C 75$ - ethyl alcohol - 25$ 80°C 58 % ethyl alcohol - 62$ 70°C 15 % - methyl alcohol - 85$ Distilled water was used in each case and ordinary commercial alcohols and glycerine. The high temperature and the vapor from the boiling liquids quickly deteriorated the corks and some evapora- tion occured,but the temperatures were carefully adjusted before each trial. If care was taken not to add too many phials, at a time, the temperature variation could easily be kept within ,5°C. The phials were kept dry and clean inside and were warmed before loading, to hasten the change in temperature to that of the bath. With the high temperatures and short periods of heating this became an important factor. This makes it difficult to determine what the actual heat experienced by the embryo, was. This difficulty, how- ever, has been experienced by every investigator of temperature in its effect on seeds. The conditions were uniform for each type of corn and should introduce no error here. In an effort to determine the speed of this temperature rise, phials fitted with thermometers were inserted in the bath and the time required to reach certain temperatures was noted. At first the temperature rise was very rap- id, but gradually slowed up until it was difficult to determine its rate of rise, so slowly did it change. An average of about 15 min- utes was required for empty phials to change from 28°C to 99.50(3. Starting at 28°C - 40OC was reached in 24 sec. 90°C was reached in 4 min. 99.5°C was reached in 14 min. 30 sec. , < , • • , . , * - . . , - 21 - When the phials were loaded the rise in temperature was even slower than in the case of empty phials. With a load of 25 kernels, 97.5°C was the average temperature reached at the end of 15 minutes. After the corn had been heated the phials were removed from the bath and the corn immediately placed in small aluminum dishes to cool. The corn was then placed in rag dolls to germinate. The rag dolls used were of two kinds; one made from a strip of un- bleached muslin, 12x56 inches and marked into 6 spaces 6x4 inches, each space to accomodate 10 kernels. This kind was used very little The kind most used was made of a good grade of bleached muslin, 8|- x48 inches, issued by the State Council of Defense, during war time. Six lots of 10 seeds each were placed in one rag doll thus giving ample room for germination and growth. The dolls were thoroughly washed, scrubbed and boiled, before using, insuring a certain amount cf freedom from saprophytic fungi. The modified rag doll as described by Duddleston (1920) was used onty where the relative degree of infection was sought for. The ordinary unwrapped method proved adequate to show germination vigor and was much quicker and cheaper than the modified method. The dolls were placed in luke-warm tap water and allowed to soak for 10 hours. They were then removed and allowed to drain thoroughly and placed in gallon jars provided w'ith drainage, and other jars placed over them. (Fig. 6) This arrangement proved satisfactory and convenient. These germinators were placed in a temperature case with the temperature accurately regulated at 30°C. Haber landt (1874) gives the optimum temperature for the germination of corn as 34.0°C and Lehenbauer (1914) says the optimum temperature for the growth of maize seedlings is between 29° and 32°C. But the advantages of the constant temper- ature and the fact that the temperature case was a permanent part of / Figure 6. Germinator jars. Figure 7. Hag dolls, showing wire cores, and a Daily Variation test, ready to read. -23- the laboratory’s equipment outweighed the disadvantage of building apparatus to make possible a slight raise in temperature to the op- timum. After 5 days (including the soaking period), at 30°C , the rag dolls were opened and read for amount of germination and length of plumule, (Fig. 7) It is realized that the rag doll is not an ideal method of germi- nating corn, but it is the quickest, best method of handling a large number of germinating kernels in a way that would make the results comparable to those obtained by the farmer in testing his corn. Every method has its disadvantages but those of the rag doll seemed least, it being readily available, compact, quickly and easily handled, and tends to familiarize one with a method much used throughout the country. It was noticed that the outside of the rag doll gave slight ly poorer germination than the inside and that the lower part of the rag doll gave poorer germination than the upper part. The wire cores, (Eig. 7) on which the rag dolls were rolled prob- ably gave as great aeration to the inside of the dolls as the outside . This, coupled with better moisture conditions gave better germina- tion on the inside than the outside.. Too much moisture caused a lower germination in the lower part of the rag doll than in the upper part. These variations, however, acted equally upon all three types and did not introduce an error in the results. Waggoner (1917) has shown clearly, one of the reasons for the dis- crepencies in the results obtained by earlier investigators on the effect of high temperatures on seeds, namely; the method used in heating. In his own work he has shown the decided difference in the effect of heat on viability when the seeds were heated in an open oven or in flasks. In order to determine whether this difference held also for the types of corn under investigation, air— dry corn . « . . . . , . , . * < - -24- was heated at 70°C for 100, 120, 140 and 160 minutes in phials as al- ready described and also in large test tubes, 26 mm. in diameter and 150 mm. long. These test tubes we re given several turns of electri- cians friction tape around the top so as to make them fit the openings in the boiler tightly and more tape was used to seal the tube in so as to prevent the escape of steam from the bath. These test tubes quickly reached same temperature as the bath and the corn to be treat- ed was placed in small wire baskets and lowered into these tubes. The corn was thus in a dry heat equal to the heat applied to the phials and was treated the same length of time in each case. In the one case there was much space for the moisture to escape from the kernels while in the case of the phials fitted with capillary tubes a very limited amount of moisture could escape. Table IV gives the significant results of a test conducted with air dry corn at 70°C Table IV. Open test tubes compared with phials, at 70° C. with air- dry corn. Type Percent of Germination of Corn 100 Min . 120 Min . 140 Min . 160 Min . Average T * P T P T P T P T P PCB SO 80 100 30 SO 70 100 30 95 .0 52.5 FOX 100 40 80 50 60 20 60 13 75 .0 30 .5 PCG 100 70 100 50 100 10 100 20 100 .0 37 .5 Average 90 .0 40 .2 *T — refers to the o pen test tubes . P— r efers to the p hials . Type Leng th of Plumule of Corn 100 Min . 120 Min . 140 Min . 160 Min . . Average T P T P T P T P T T> X PCB 113 48 100 51 80 19 91 7 96.0 31 .5 FOX 71 7 76 15 29 10 42 8 54 .5 10 .0 PCG 118 49 98 13 81 13 91 13 97.0 21 .8 Average 82.5 20.8 -25- Waggoner (1917) states that the chief factor determining the re- sistance of seeds heated to the same temperature by different methods is the amount of moisture absorbed or lost during the treatment. On this basis the results given above are undoubtedly more significant than they would be at a higher temperature, because the long heating period allows much moisture to escape before injury or killing takes place. At high temperatures and short heating periods it is doubt- ful if any such difference would be noted. The average difference of 49.8 percent in germination and 61.7 mm. in length of plumule, and the consistently lower percent of germination and length of plumule of those kernels heated in phials, at all temperatures used, show con- clusively the difference due to method of heating. The corn after it was heated was immediately placed in aluminum dishes to cool. Sometimes it was more convenient to allow the corn to cool in the phials in which it was heated. This was not done, on the theory, that the after effects of the heating would continue much longer if the corn remained in the phials than if it was placed in the dishes to cool. To test this point, air dry corn was heated to 90°C for 4-7 minutes, one series being allowed to remain in the cork- ed phials to cool, and the other being placed in the aluminum dishes to cool. The percent of germination of those cooled in the phials was 60.8 percent while the percent of germination of those cooled in the dishes was 65.0 percent, a difference of 4.2 percent. Simi- larly the difference in plumule lengths was 23*3 mm. in favor of those cooled in the aluminum dishes. To avoid the necessity of raising the temperature of the entire phials, its contents, the stopper and capillary tube to the temper- ature of the bath, it was thought desirable to construct an appara- tus which would allow the temperature of the phial to be raised to . « • • •„ f . . , . . . « #: i . , * . , '■ J - 26 - the temperature of the bath before being loaded. This was done by replacing the capillary tube by a large glass tube of 12 mm. inside diameter. The phial was then placed in position and allowed to come to the temperature of the bath. The 10 kernels to be treated were placed in a glass tube of the same size as that used in the phial and in loading , the kernels were allowed to slide from the glass tube, down into the phial. This was done very quickly and the tube leading into the phial was then closed with a capillary tube to make conditions comparable with the ordinary method of heating. A similar glass tube, enlarged to a funnel form at the top, was passed thru an opening in the top of the electric oven and aluminum dishes were loaded without opening the oven door, thus avoiding a drop in temperature. There seemed to be no consistent difference between the results obtained by using this loading device and the ordinary method of placing the kernels in the cool phial and then placing in the bath, hence it was not used except in a very few cases. -27- IV .RESULTS AND DISCUSSION. EFFECT OF HEAT ON AIR-DRY CORN. No extensive work has been done on the time and temperature re- quired to injure or to kill corn by subjecting the kernels to heat. Almost without exception, where any time and temperature are given, no mention is made of the moisture content of the corn, though it has been known for many years that the drier seeds are the greater degree of heat they can withstand. Miss White (1909) in her studies on fer- ments in seeds, heated corn at 99-100°C for 6j? hours and got no ger- mination, while corn heated for one hour to 122° and 124°C was killed Burgess (1919), in investigating possible injury done to the vitality of seeds by heat treatment for insect pests, found that corn gave 68 percent germination when treated at 176°F (S0°C) for 1 hour, and 32 percent when treated for 3 hours. Montgomery (1917), investigating a similar problem said, “the germinating quality of grain is destroy- ed at 150°F (65.6°C) and probably injured at 5° less, if long ex- posed.” Ear corn hanging in a seed room which was disinfected sever- al times at 140°F (60°C) for several hours at a time, was not appar- ently injured. All of the work which has been done, and it is small in amount, is of the same fragmentary nature as that reported above. Thus it seemed the first task to find out the exact time and temperature re- lations of air-dry corn, under the conditions of the experiment, namely; dry heat, applied to corn in phials fitted with capillary tubes, the volume of the phial being about 8 times that of the corn. It should be borne in mind that the moisture content of air-dry corn, as kept in the laboratory, averaged; PCB-10.93 percent, Fox- 10.64 percent, and FCG-10 ,41percent . These percentages are based < . , - . ' . . • . < -28- on the air-dry weight of the seed and were determined as discussed below. It is for corn of the above moisture content , that the time and temperature figures given in Tables V, VI, VII, and VIII, a.pply. Altho the moisture content of the corn varied somewhat, it was lower than if it had been stored out of doors, subject to varying climatic conditions. The average of many moisture determinations made on samples from all over the state, by the Division of Crop Production, College of Agriculture,Univer sity of Illihois, is as follows: for samples re- ceived and tested in February---15 percent, March-15 percent, and April-12 percent. These figures should not be lost sight of in the drying of corn, or in heat treatments for insect or fungous pests. Table V. Air-Dry Corn - 100°C - Dry Oven. Types of Corn Percent of Germination Min. 7 £ Min. 10 Min. 12£ Min. 15 Min. Average PCB 184* 100 24 44 0 0 53.6 Fox 71 88 56 0 8 0 50.4 PCG 77 92 72 52 4 0 40.0 Types of Corn Length of Plumule ( in mm. ) 5 Min. 7 * Min . 10 Min. 12£ Min. 15 Min. Average j PCB 184 108 19 11 0 0 27.6 Fox 71 102 71 0 7 0 56.0 PCG 77 152 112 14 4 0 56.4 ^•-refers to number of ear used. M ith vaanii icmrawg*: -29- The corn heated at 1C0°C as given in Table V, was heated in the electric oven in open aluminum dishes. This accounts for its not being killed except after 15 minutes exposure, while the same kind of corn is killed in 9 minutes at 90°C when heated in the phials , This illustrates again the difference due to method of heating. At 100°C the period required to kill, when the phials were used, was so short that it was difficult to get results which were of much value, especially in view of the slow rise in temperature in the phials, as discussed under Methods. Only a few minutes were required to kill when 100°C was used, and the actual temperature experienced by the seed at the end of this time was undoubtedly far below 100°C, Table VI. Air-Dry Corn - 90°C - Phials. Type of Percent of Germination Corn CHECK 3 Min. 4 Min. 5 Min. 6 7 Min. Min. 8 Min. 9 Min. Average PCB 100 100 90 90 30 70 10 0 55.7 Pox 100 90 100 90 80 70 0 0 61.4 PCG 100 100 100 80 60 70 20 0 61.4 Type of Length of Plumule (in ram. ) Corn CHECK 3 Min. 4 Min. 5 Min. 6 7 Min. Min. 8 Min. 9 Min. Average PCB 132 118 114 98 58 103 5 0 70.9 Pox 107 119 94 101 96 52 0 0 66.0 PCG 135 126 122 98 68 89 51 0 79.1 -31- When 90°C was used and the corn treated in phials, complete kill- mg took place at 9 and 10 minutes while injury to germination was manifest at 5 minutes. A slight decrease in plumule length, already noticeable at 3 minutes exposure, when compared to the check may be due to retardation of germination and growth caused by heating, or it may be due to heat injury. It is possible that the corn heated for 3 minutes would finally overcome the retardation of its growth, a.nd give as great a growth as the check. No studies were made on this point, but it is noticeable throughout this entire investigation, as it is in Tables V, VI, VII, and VIII, that the length of plumule at the end of 5 days is much less from those seeds heated for a longer period than in those not heated so long. Much of this is due, I am convinced, to actual injury done by the heat, which the plant can never overcome. In any case, the effects of heat are more quickly noticeable in length of plumule than in percent of germination* Care must be taken, however, to draw conclusions only from consider- able numbers because of the greater variation in plumule length, than in percent of germination* The average of other series run at 90°C give germination percents! of PCB-68.8, Pox-60.3, and PCG-64.5, showing that PCB is not always lowest in percent of germination, though this is usually the case. Air-dry corn heated at 80°C in phials, is practically all killed after 20 minutes and all killed after 25 minutes exposure. Injury is already noticeable after 10 minutes exposure. A limited amount of work does not allow me to give the exact length of time required to kill at 70°G, though injury is apparent after 80 minutes exposure. A series which was made unuseable by being read too early, indicates that after longer periods of ex- posure (160 and 180 minutes) the Pox and PCG corn is almost ■MtaaniwaiMij— uy . 1 i npiaim w o 1 1 11 ■ i i w n o i miiii n w i i > ■ ■ .n - , ■— 1 ' . . < . , < t ' , « « . , . , . • • , ■ • t « 4 , . , . -32- completely killed while the PCB corn germinates 50 and 30 percent. The whole series averages; PCB-55.0 percent, Pox-28,3 percent and PCG-26.7 percent, with the plumule lengths in a similar ratio. This behavior is similar to that experienced in the heating of desiccated corn, discussed below. It further resembles the results obtained on heating desiccated corn, in that the differences in resistance are most noticeable at lengths of exposure which are highly injurious. This is borne out by the results given in Table VIII where the re- sistance to heat is exactly opposite to those obtained at 80, 90, and 100°C. PCB Pox PCG Thus: 70°C 70,0$ 6670$ 54.0$ Average :80°C of :90°C :100°C 30 . 9$ 43.3$ 48.9$ This may be due to the greater amount of water given off during the lohg heating process, by PCB, than by the other two types of corn and its consequent greater resistance to heat. The average of results for 80,90 and 100°C given above, justifies the statement that air-dry PCB corn contains the most moisture and is least resistant to heat, PCG corn contains the least moisture and is most resistant to heat, while Pox is intermediate in both moistur content and resistance to heat < - 33 ” DESICCATION. From the earliest investigators down to the present time, increas- ing importance has "been ascribed to the moisture content of grains as affected by high temperatures. As a result, most recent articles, with some notable exceptions; dealing with the effect of heat on via- bility are careful to state fully the conditions of the experiment; the seed used, the method of heating and the moisture content of the seed. Waggoner (1917) has summarized the earlier work on the relatior of moisture content to viability of seed heated to different degrees, and his own work is the first detailed, quantitative piece of work, using one kind of seed. He has shown that the resistance of seeds of radish, exposed to high temperatures, is inversely proportional to their initial water content at the time of heating. The purpose of this part of the investigation, then, was to deter- I mine to what extent this was true of corn, to ascertain the actual time and temperature relations of corn desiccated for various periods of time as compared with air-dry corn and to determine if the three types of corn used, responded similarly to this treatment. Two quart mason fruit jars were fitted with rubbers and tightly fitting screw covers. Hooks were soldered into the middle of these covers, from which hung paraffined wire baskets filled with corn. (Fig. 8.) About 150 c.c. of concentrated sulphuric acid (sp.gr. 1.84' was placed in the bottom of each jar as the desiccating agent. Each of the three types of corn were thus lowered in water content and at intervals corn from these baskets was tested to determine its re- sistance to heat. Sets of these jars were started at intervals in order to have a succession corn of different moisture contents for a series of trials. These jars were placed in a 30°G constant tempera- ture case and were removed only while being tested. As the length , . , « < . « . . « - 34 - Figure 8.- Desiccator, with corn in wire basket suspended over sulphuric acid. -35- of time of desiccation increased, the temperature used was increased and the time of exposure lengthened. The results of trials at various times and temperatures, after desiccation of 1,2,4,6,8,9,10,12,14,15, 17,20,23,27,31 and 100 days are given in Table IX. The results are expressed as percent of germination and these are averaged at the foo of the table. Those treated at 80°C are grouped in the lower left hand corner of the table, those at 100°C in the upper right hand cor- ner and those at 90°C in the middle of the table, each set of results being divided from the others by a heavy zig-zag line. . Thus the three types of corn which had been desiccated for 8 days were treated at 90°C for 35,40,45 and 50 minutes and also at 80°C for 100,110,120 and 130 minutes, and the percent of germination for each given in its proper place. , . I ( ( I . . , , < . TaAo/e IK Pzrcar?! ol 6&r/77//7&f/&/7 20 Pa V 23 Payo 27 a bj /3 3/ PayT) ZOO Day 3 <0 ¥ X 'O t i l $ \ k l $ k k % ?> 1 k * l l $ \ l $ •* k l $ 1 l $ k l SS $ $ k 1 * * l * 1 fQ \ ' \\ » f] 90 90 700 IOO 80 zoo Jtl 10 50 90 <30 50 707) 60 707? 90 90 80 50 50 7i\ r 2 Itf J5_ nr ZOO 80 30 too 90 80 20 20 /O 90 70 70 00 0 ZO 40 O 70 60 20 30 90 70 90 90 30 30 lo &0 50 70 O O O 70 30 40 O 70 o ZO O 70 70 O 70 30 40 40 ??$ 25 65 30 ZO 70 70 20 30 60 70 <30 60 90 O O 75 0 o 70 30 O O — 90 ZO 20 2)0 50 O O 70 40 40 700 50 70 80 50 80 0 o O 0 O O 40 ZO 70 40 30 50 80 30 60 'X 60 20 30 90 40 90 60 60 60 90 60 80 - 70 70 O 80 70 30 70 40 90 40 30 O /O 90 70 30 90 30 40 700 50 60 80 /O ZO 86 O 50 45 90 - 30 90 90 90 40 0 O - - 39 50 50 40 80 90 50 80 40 O O 55 90 60 70 50 O 30 60 9i 2! h 70 30 50 80 30 50 60 O O 65 90 30 20 80 60 70 10 /OO 30 80 60 30 20 65 30 30 zoo 60 70 75 ZOO 30 90 zoo 90 ZOO 50 20 50 80 60 80 90 70 700 60 700 30 90 50 70 30 50 70 40 80 80 50 65 /OO 90 30 IOO 70 30 80 60 70 90 90 70 80 20 40 40 40 - 60 too 90 70 95 70 O 50 HO y< 9' 'C. ZOO 80 ZOO 50 20 ZO 60 o 70 JJ5 120 90 40 90 700 80 700 20 /O 20 70 o o 80 70 40 J25 70 40 70 J30_ 90 60 80 OO o o 135 90 60 60 145 80 60 60 !5o 90 60 30 70 90 30 J55_ 80 60 70 /60 Jpp 60 ZO ZO Jpp 195^ 125 qZ — 90 ZO ZO 70 60 O ZO O o 70 40 40 70> o o 80 50 30 ZOO 60 30 V5 75.0 195 47.0 GOO 520 36.1 61.1 6U 775 463 550 863 57./ 79.4 86.6 56.6 700 90.0 55.0 775 609 355 47.7 46.6 77.9 964 667 o 3.3 47.5 5.0 25 675 675 775 767 369 769 64.5 745 345 78.7 133 99.6 633 60.0 433 -36- Difficulty was encountered in determining the proper time and tem- perature to use in testing the corn. As desiccation steadily de- creased the moisture content, the time and temperature of treatment had to he increased in order to he injurious, and thus give signifi- cant results. With the lower temperatures this change in time was rapid, as shown hy the similar results obtained after 1 days desic- cation, hy exposure to 80°C for 15 minutes and after 4 days desicca- tion at 80° C for 85 minutes. With the higher temperatures, however, this change was slow, as shown hy the very similar results obtained hy exposure to 100°C for 20 minutes after 12,14 and 17 days dessica- tion. As a result of this constantly changing resistance of the corn to heat, much of my early work was of little value, except to indi- cate the proper tine and temperature to use for corn desiccated the same length of time. Hence the need for a succession of desiccations in order to get significant results* It is very evident from Table IX, that corn desiccated “2" days, con- taining 8.78 percent moisture, and killed at 90°C for 20 minutes, is very much less resistant to heat than corn desiccated 23 days, con- taining 5.75 percent moisture, and giving a germination of 63.3 per- cent after 90°C for 3|- hours (225 minutes). Similarly corn killed at 100°C for 30 minutes containing 6.11 percent moisture after 14 days desiccation, is much less resistant than corn, containing 2.16 per- cent moisture after 100 days desiccation, giving 63.3 percent germi- nation after exposure to 100°C for 2£ hours (150 minutes). This re- lation existing throughout the table justifies me in saying that, without regard to the type of corn used the resistance of corn to heat varies inversely as its moisture content at the time of heating. Probably the most significant fact brought to light by the desic- cation study is the varied response of the different types of corn -37- to the treatment. Beginning with the first day of desiccation and continuing throughout, (100 days), the percent of germination of PCB after heating is much higher than either Box or PCG , while Pox is somewhat lower than PCG, which occupies an intermediate position throughout. The averages of Table IX are brought together in Table X and make these differences more evident. Table X . Averages of Percent of Germination of Bes iccated Corn. Types of Corn Bays of Besiccation L Bay 2 Bays 4 Bays 6 Bays 8 Bays 9 Bays 10 Bays 12 Bays 14 Bays PCB 92.5 42.0 86.1 77.5 86.3 86.6 90.0 60.9 46.8 Pox 75.0 60.0 86.1 46.3 57.1 56.6 55.0 35.5 22.9 PCG 79.5 52.0 61.1 55.0 79.4 70.0 77.5 42.7 36.4 Types 15 D 17 B 20 B 23 B 27 B 31 B 100 B Average PCB 66.7 42.5 87.5 76.7 64.5 78.7, 63.3 71.8 Pox 0 5.0 67.5 38.9 24.5 23.3 80.0 48.7 PCG 3.3 7.5 72.5 28.9 34.5 59.8 43.3 50.2 < -38- Using the percent of germination of PCG as zero, the difference between PCB and PCG is plotted in Fig. 9 as a solid line while the difference between Fox and PCG is plotted as a broken line. Thus at 12 days, PCB has a germination 18.2 percent higher than that of PCG, hence it is plotted as+18.2, while Fox has a germination of 7.2 percent lower than PCG, hence it is plotted as -7.2. In only one instance, (2 days) does PCB have a lower germination than PCG and Fox a greater germination than either, while Fox quite consistently shows a lower germination than PCG, though not as much lower than PCG, as PCB is higher. The average of all germinations of desiccated corn are; PCB-71.8, Fox-48.7, and FCG-50.2 percent. The difference in germination in favor of PCB is most visible where the temperatures are highly injurious; as for example: the 90°C series at 15 days, the 100°C and 90°C series at 17 days, and the 100°C series at 27 days, where almost complete killing occured in both PCG and Fox while PCB gave a fair percent of germination. The differences are not so great in series such as that of 80°C at 4 days, where the time of heating was not long enough to be injurio and the differences may even be in favor of PCG or Fox, where very little heat is applied, due probably to the superior vitality of PCG when not affected by too high a temperature. This may be seen in 90°C for 5 minutes after 2 days desiccation and in 100°C for 5 min- utes after 12 days desiccation and in many others not included in the table, such as a series at 80°C for 10-35 minutes after 2 days desiccation where the average percent of germination was; PCB-80, Fox-88, and PCG-92; 10-35 minutes being altogether too short a time to produce injury. G e /P/w/ /v' a Tv on/. -41- Table XI brings together the average plumule lengths of the corn treated after desiccation. Although it does not in all cases follow Table X yet the relative ranking of the types is very similar to that of the percents of germination. The average of all plumule lengths shows that PCB corn has the greatest plumule length, Fox the least, and PCG intermediate, thus having the same ranking as the per- cent of germination. Some difference of opinion has existed and probably still exists, concerning the effects of desiccation on the viability of seeds. Some investigators, notably Ewart (1897), have held, that it is im- possible to reduce the moisture content of the seed much below 2 to 3 percent of air-dry weight without affecting germination injurious- ly. In the face of more recent work it is impossible to hold to this opinion concerning all seeds. The work of Waggoner (1917)y Ha.rrington and Crocker (1918) and Walker (1922) have shown that some seeds can be reduced to a very low moisture content without injury to their viability. The work of earlier investigators along this line, has been reviewed by Harrington and Crocker (1918) and need not be reviewed here. In their own work they carefully dried sever- j al kinds of seeds, in vacuo over CaO and over concentrated sulphuric^ acid. They reduced the moisture content of Kentucky blue grass seed!; to 0.1 percent and then heated it for 6 hours at 100°C , reducing it still more. The seed thus treated gave a slightly lower germination (5 percent) though its germination energy was considerably reduced. The germination of barley and Sudan grass was not lowered by drying though the moisture content was reduced to 0.5 and 0,6 percent, Johnson grass was slightly injured by being dried to a moisture con- tent of 0.1 percent. Wheat with moisture content reduced to 0.9% was not injured. , . . * - * . . * , ■ " ' - LO C - . c * < . , , . « • , , . « . . MOISTURE DETERMINATIONS -43- In order to know definitely the amount of moisture present in the corn used and the exact effect of drying on this, it was necessary to make a series of moisture determinations of air-dry corn, and that dried for various periods of time. Two determinations w r ere made in November by the Division of Crop Production on 100 gram samples, using the Duvel method, resulting in; Fox-10.4 percent and PCG-10.0 percent. All subsequent determinations were made by placing the corn (10 kernels) in weighed aluminum dishes and reducing to con- stant weight in an electric drying oven at 100°C. Because of a slight variation in temperature between the two shelves of the oven, it was attempted to keep all samples on the same shelf to do away with any error which might exist, due to that cause. The dishes were cooled in a calcium chloride desiccator and weighed at intervals of 1 day until found constant in weight. This frequently took as long as 10 days. Table XII. Moisture Determinations of Corn, Air-Dry and Desicca/ted Time of desiccation in days. Type AIR-DRY 1 Day 2 Days 4 Days 6 Days 8 Days 10 Days 14 Days 17 Day PCB 10.93 8.87 8.09 7.87 7.28 7.49 6.19 5.98 5.70 Fox 10.64 8.77 8.97 7.79 7.74 7.56 6.46 6.32 6.28 PCG 10.41 9.23 9.28 7.70 8.43 7 . 22 7.73 6.05 6.87 Type 20 Days 25 D 27 D 72 D 82 D 100 D 115 if 115 D^ 115 Df PCB 6.60 5.53 5,02 3.76 2.88 2.23 2.20 2.05 0.73J* Fox 5.94 5.77 4.69 3.32 3.00 1.92 2.37 • • • • 1.19 PCG 5.79 Ju9£-.. 6.30 3.04 3.17 2.40 2.45 2.35 1.16 *-70°C-30 hrs . T- t*-Des. 117 days, 70°-60 70°-60 hrs . hrs , £-70°-60 hrs, 98°-32 hrs. 98°- 20 hrs. -44- In Table XII are given the moisture determinations made on the air-dry and desiccated corn. Tne figures are based on single deter- minations, except air-dry - 5 determinations , and 8 and 10 days - 2 determinations each. The moisture is expressed in percents, based on the air-dry weight, and not on the dry weight. Reducing Table XII to a graph, (Figure 10) the moisture relations! of the three types of corn can best be expressed by showing relative water loss after different periods of desiccation, up to 27 days. The moisture contents, of the three types of corn, after 72, 82 and 100 days of desiccation is shown at the right of the graph. It will be noted that there is a fairly steady decrease in the moisture con- tent. PCB contains the most moisture in the air-dry condition but soon falls to the least and remains there fairly constantly; PCG contains the least moisture in the air-dry condition but rises to the most, and Fox, maintains an intermediate position. The 15 moisture determinations, from 1 to 115 days, inclusive, given in Table XIII may be grouped according to frequency. That is, the number of times, out of these 15, that each type of corn, con- tains the least, medium and most amounts of moisture. This results in: Least Medium PCB 8 4 Fox 3 10 PCG 4 1 This is graphically shown in Figure 11, the black spaces indicating the number of times each type of corn contains the least; the clear spaces, the medium amount, and the cross-hatched spaces, the great- est amount of moisture. Most 3 2 10 The differences in amount are not large however, the average of -45- all desiccations "being; FCB-5.71 percent, Fox-5.79 percent and PCG- 6.11 percent, giving differences of .08 and .32 percent respectively. ■ < . . • f~/G- UffC /O. /tfotSTUffE Z3CTfE>/v)/iV4r/o/vs — Arr-e/r i> / rr^f? r/vr f*er?/ox>$ or z>es/ cc /* T/o/v. - 47 - FlGUf?E/l' Moistore. Dere/m/MAr/oAss - /^/p^q p/vcy pv/ry wy/cy FACH Tyre OF COf?M COATA//VS 7F£ /.FAST, A* 0 ST, AMD Af FT>/U AT A Ml OO/vTS oF AA 0 'S T u t? £ . K\\\l — MOST MFD< OAA GRADIENT OF DESICCATION. In the process of desiccation, wii-h the corn in long wire baskets suspended over acid and with the bottom of the basket within 15 mm. of the surface of the acid and the top within 115 mm. of the surface, it seemed natural to question whether desiccation was exactly uni- form throughout the column of corn. In view of the methods some- times used to secure moisture or desiccation gradients over water, salt solutions, or mixtures of sulphuric acid and water in open vessels , it was necessary to determine whether complete uniformity of desiccation occured throughout a tightly closed vessel. The same paraffined wire baskets as in desiccation were used and only PCB corn experimented with. These desiccators were placed in a 30°C con- stant temperature case and the corn used after 8,9, 12 and 16 days desiccation. When ready for treatment, the corn was divided into 3 parts by sticking short pieces of copper wire thru the column of corn at the proper places until they formed a network which held the corn so the upper 1/3 could be removed. Each third was then placed in wire baskets in desiccators so it would not absorb moisture while being tested. Each third made about 12 lots of 10 kernels each which were tested at the proper temperature for periods of time known to be injurious. Thus after 16 days desiccation, each third of cornj was heated, 10, 11, 12, and so on up to 22 minutes. Corn desiccated; 8,9 and 12 days was heated at 90°C while corn desiccated 16 days was heated at 100°C. The results of these series are summarized in Table XIII. . . . « « , . . . , < . 1 Table XIII. Desiccation Gradient of PCB Corn Summary . --- = Position in Desiccator Percent of Germination Length of Desiccation in Days. 8 9 12 16 Average Upper 84.0 70.9 35.5 70.8 65.3 Middle 75.0 63.3 37.7 68.5 63.6 Lower 66.0 60.0 32.2 68.5 56.6 Ratio of Upper to Lower 18.0 10.9 3.3 2.3 8.7 Position Length of Plumule (in mm. ) in Length of Desiccation in Days Desiccator 8 9 12 16 Average Upper 78.0 67.1 59.3 78.8 70.8 Middle 73.0 60.0 69.0 79.2 70.3 Lower 72.0 70.6 53.6 75.2 67.9 Ratio of Upper 6.0 3.5 6.3 3.6 2.9 to Lower -50- From the data in Table XIII it is evident, that the corn from the upper 1/3 of the basket, which was furthest from the surface of the acid, was the most resistant to heat, and that from the lower 1/3, closest to the acid, was least resistant. To reduce to a single figure the difference in germination between the upper and lower parts, the percent of germination of the lower was subtracted from that of the upper and the figures given at the foot of each section of the table. These figures indicate that after 6 days desiccation the corn in the upper 1/3 gave 18.0 percent better germination after heating, than that in the lower. With increased desiccation, this difference became less until after 16 days it was only 2.3 percent. It is probable that it would slowly approach zero as a limit sc that with time the desiccation would become uniform throughout. Data are not available to indicate what the ratio would be following 1 to 8 days desiccation, but it is probably that it would describe a regu- lar curve, there being little difference after a short period of drying, this difference increasing rapidly to a climax and then slowly decreasing again to zero. The length of plumule varies more widely, as is usual, but the averages rank the same as the percents of germination. The ratio of upper to lower shows little difference throughout the series, but its average is in favor of the upper by 2.9 mm. As the same amount of corn was used from each of the baskets at each test (in testing resistance after desiccation), the top of the column of corn was approximately the same distance from the surface of the acid, therefore, the error introduced by a difference in height above the desiccating surface would be negligible. One kind of corn (PCB) only, being used, the difference in be- havior of the upper and lower parts of the basket must be due to . , , ' , , . , * , -51- differences in moisture content. To determine what difference exist- ed, moisture determinations were made of corn from the upper, middle and lower parts of the basket, with the following results: Upper 5.70 percent Middle 6.03 percent Lower 6.30 percent This gives a difference cf .60 percent in favor of the upper, which further supports the statement that the resistance of corn to high temperatures varies inversely as its water content at the time of heating . . . : im i . . -52- DAILY VARIATION. It was readily noticeable, in the heating tests, that varying re- sults were obtained on successive days, even tho the same type of corn, the same heat, and the same period of exposure was used. This seemed to be correlated with climatic conditions out-of-doors-humidi- ty, and as the ventilators in the laboratory were open part of the time, the laboratory air varied in humidity also. To simulate con- ditions under which corn would be stored in open cribs on the farms of Illinois, shelled corn of the three types was placed in wire bas- kets and hung out-of-doors, under a roof-like shelter suspended on a wire strung between two wings of the greenhouse, and open to all air currents, but protected from direct sunshine and from rain. Tests made on this corn at this season of the year will serve as a guide in treating crib corn during the rainy spring season, for fungous or insect pests by means of heat, and give the limits of time and temperature beyond which injury to germination would result Furthermore it was desireable to find out if the variation in the same test from day to day was due to variation in relative humidity of the air, and, if so, how rapidly and to what extent this varia- tion in moisture content followed the variations in humidity. The variation in moisture content of the corn was not measured directly but was measured by the variation in percent of germination follow- ing heat treatment, a low germination indicating a high relative humidity, hence much moisture in the corn, and vica versa. A check test was made on the air-dry corn just before it was hung out-of-doors (on March 28) and at intervals afterward up to April 26. Each test consisted of a check and 10 kernels of each type of corn heated at 90°C for 3, 4, 5, 6, 7, 8, and 9 minutes. The percent of * , . ' . . , I . ' t t c • -53- germination of each type of corn after these exposures were added and these totals used to construct the graph shown in Figure 12. Thus on April 2, PCB , Fox and PCG corn from the baskets hanging out-of-doors was tested at 90°C with the following result in germination: 3 4 5 6 7 8 9 Check Min, Min. Min. Min. Min. Min, Min. Total PCB 100 100 70 50 40 0 0 0 260 Fox 100 90 90 80 30 0 0 0 290 PCG 100 90 70 60 30 0 0 0 250 The total does not include the check, which did not vary. This was done at each test and these totals are summarized in Table XIV. Table XIV. Totals of Germination - Daily Variation, March Aioril Type of Corn Check 28 29 30 1 2 5 6 8 9 11 PCB 390 1 250 210 210 260 120 130 180 140 130 Fox 430 300 280 290 290 210 180 140 230 180 PCG 430 340 280 240 250 130 180 90 220 270 Average 417 297 257 247 267 153 163 137 197 193 Type of Corn 12 15 16 17 19 20 22 23 24 26 PCB 200 180 120 180 220 160 180 200 203 140 Fox 250 250 230 180 240 270 280 340 260 200 PCG 220 220 160 230 220 230 200 260 290 170 Average 223 217 170 197 227 220 220 267 251 153 4 4 \ # 4 5 3 3 3 3 A Z A A z / / • /• Cr£L PM M/a T/h/l / r> Sf* ^ cP *5 ** /ve-a/p£ / ? 340 y/f 3 to ?6 r /° T *‘- JiEffA\/A/AT/04 ffelATtvE 1 r M ■) >■ * lATiot v or // u /v» / d rrjr a \/*Z> Ge., <0 '/v\//va r/OA/ -54- The data on relative humidity was obtained from the Division of Soil Physics. In this Division daily relative humidity readings are taken at 7 A.M., 2 P.M. and 7 P.M. My heating tests were not made coincident with the observed readings but the nearest humidity read- ing was taken as the one to be graphed. Thus if the corn was tested at 3 P.M. on April 2, the relative humidity reading taken on that day at 2 P.M. was the one used. In Figure 12, the red line indicates the relative humidity and the black line the average of the total germinations. It was found, upon graphing the germination totals for each type of corn separate- ly, that no type followed the changes in relative humidity more closely than another. For the sake of clearness, therefore, the totals for the three types were averaged and the graph made from this data. The variation of the three types followed that of the relative humidity closely where the changes were great and continued for several days, such as the big drop from April 2-5 and the drop from April 23-26, but where the changes were smaller and less pro- longed, as April 11 and 12, one type would follow the change in re- lative humidity while the other two types would vary in the opposite direction, or vica versa. We are not justified, from the data at our disposal, therefore, in saying that one type varies more widely or more rapidly under out-door conditions than another. But we can say; that, with few exceptions, the average resistance to heat of corn stored in the ope: changes inversely as the changes in relative humidity of the atmos- phere. The places where the curves do not coincide the differences are not great and could probably be explained by a wide change in humidity before the test was made, or, probably better, by the corn lagging behind the changes in relative humidity of the atmosphere. ->55- The germination totals of PCB were low, those cf PCG , high, and thoee of Fox intermediate. This relation held quite consistently throughout the entire test. A graph of the average total plumule lengths varied more widely than did that of the percent of germination and did not follow the changes in relative humidity as closely as did that of the percent of germination, hence was not included in Figure 12. A moisture determination was made on April 26, at the time the test was made. The day was warm and humid and the corn fell on the table with a dull thud, while being handled. From the graph we see the humidity was low,, but not the lowest reached during the test. The moisture determination was as follows: PCB - 14.86 percent Fox - 14.60 percent PCG - 14.44 percent This bears our the statement that PCB, in the air-dry condition, contains the most moisture and Fox and PCG lesser amounts in the order named. The average total germination on this day was one of the lowest in the table. -56- PLACINC- III WATER AFTER HEATING. Just (1875) in working with seeds of Trifolium pratense said that seeds heated at 100°C germinated if, after heating, they were sup- plied with water slowly, hut did not germinate if supplied with water rapidly. An extensive series of experiments were undertaken to see if placing in water immediately after heating to high temperatures had any effect on the germination of corn. Whether the sudden in- take of water and the sudden cooling injured the viability of the kernels. The corn was heated in phials in duplicate sets and immediately after heating, while the phials were still hot, the corn from one set was placed in tap water at room temperature , while the corn from the other set was placed in the aluminum dishes to cool. After the first set had soaked 4 hours they were taken out and placed between moist blotting paper, to prevent drying out, and the second set soaked for 4 hours, thus soaking each set for an equal period of time. At the end of the second 4 hours both Bets were placed in wet rag dolls and these placed in the germinator jars as usual. Two trials were made, involving air-dry corn heated at 80° and 90°C , corn which had been desiccated 19 days heated at 90°C and corn which had been desiccated 18, 51, 86 and 100 days, heated at 100°C , The entire result may be summarized in Table XV. Air-dry corn was averaged separately from desiccated to determine any difference in resistance, S - designates corn placed in water immediately after cooling and D - corn placed in aluminum dishes to cool. -57- Table XV. Effect of Placing in Water Immediately after Heating. Type of Corn First Trial Second Trial Air -Dry Desiccated Air-Dry Desiccated S D S D S D S D PCB 91.7 86.6 87.7 91.1 56.7 53.3 81.8 71.0 Fox 95.3 88.3 53.9 51.4 60.0 58.3 46.7 51.7 PCG 90.6 85.0 58.3 63.3 46.7 53.3 49.2 46.7 Average 91.9 86.6 66 .6 68.6 54.5 55.0 59.2 56.5 Length of Plumule , . . . — 113.0 118.4 72. 2 27.6 72.8 63.4 72.3 83.5 Prom Table XV it is evident that there is no consistent variation due to placing in water after heating. In the first trial; in air- dry corn, the germination was best in that placed in water immediate- ly after cooling, and the plumule length was least. In desiccated corn, the germination was best, in that placed in aluminum dishes to cool, and the length of plumule was least. This is exactly reversed in the second trial. The differences, moreover, were not large. We may say, therefore, that placing corn in water immediately after heating has no effect whatever on either the percent of germination or the length of plumule. -58- GROWTH IN SOIL, OP HEATED CORN. To determine the effect of heating the kernels upon the germina- tion of corn in soil and the subsequent growth and green weight of the seedling, corn of the three types was heated and then planted in rows 2x5 inches, in garden loam in a bench in the middle of the gree* house, equally lighted and heated from all sides. Air-dry corn was heated at 80°C for 5, 7-J, 10, 12J- and 15 minutes and was planted -f inch deep. Corn which had been in the desiccator for 16 days was heated at 90°C for 110, 120, 130, 140 and 150 minutes and was planted the same way. Checks of each were also planted. Ten kernels of eac? type were used for each period of heating. There was a noticeable retardation in the growth of corn heated most severely, in both the air-dry and the desiccated lots. In dig- ging up the kernels there were many which had put out a short plu- mule or radicle but did not have growth energy enough to force their way to the surface. This probably accounts for much of the differ- ence between the results obtained in rag dolls and that obtained in the soil, for the percent of germination in rag dolls was 60.0 per- cent and in soil, 27.8 percent, in a series using air-dry corn heat- ed at 80°C. Records were taken of the time of appearance of the shoots above the soil, and height measurements were taken at the end of 30 days, at which time the plants were harvested by cutting off the stalk at the surface of the soil and the green weight taken. The results of the above planting are recorded in Tables XVI and XVII Table XVI. Growth -59- of Heated Corn in Soil-Air -Dry-80°C . Treatment Type Percent of Total green Average green Height per Germinat ion, Weight weight per plant (grams) plant (grams' (cm. ) Check PCS 100 47.85 4.785 59 Fox 100 37.65 3.765 59 PCG 90 40.25 4.472 56 5 Min. PCB 100 43.00 4.300 62 Fox 70 23.10 3.300 55 PCG 90 41.97 4.663 57 7 - 5 - Min. PCB 100 40.10 4.010 54 Fox 70 31.23 4.461 52 PCG 100 55.97 5.597 64 10 Min. PCB 60 6.95 1.158 30 Fox 60 29.32 4.887 61 PCG 60 14.98 2.497 43 12-g- Min. PCB 10 0.81 0.810 28 Fox 10 0.52 0.520 24 PCG 50 7.65 2.550 37 15 Min PCB 0 0 0 0 Fox 0 0 0 0 PCG 0 0 0 0 Average PCB 67.5 22.72 2.570 43.5 Fox 52.5 21.04 3.292 48.0 PCG 70.0 30.14 3 . .8.27 5.0.3 -60- Table XVII. Growth of Heated Corn in Soil- Desiccated 16 days - 90°C. Treatment Type Percent of Germination Total Green Weight (grams) Average Green Weight per plant (grams) Height per plant (cm. ) Check PCB 100 39.70 3.970 53 Fox 80 29.35 3.670 49 PCG 100 39.25 4.242 51 110 Min. PCB 70 16.95 2.421 43 Fox 10 2.00 2.000 40 PCG 0 0 0 0 120 Min. PCB 90 33.10 3.678 48 Fox • 0 0 0 0 PCG 0 0 0 0 130 Min. PCB 60 10.00 1.667 34 Fox 10 0.47 0.470 21 PCG 0 0 0 0 140 Min. PCB 60 9.80 1.633 30 Fox 0 0 0 0 PCG 10 3.00 3.000 43 150 Min. PCB 70 14.90 2.129 38 Fox 0 0 0 0 PCG 0 0 0 0 Average PCB 16.95 2.764* Fox 4.0 4.92 1 . 235* 12.2 PCG 2.0 .60 3.000* 8.6 ^Average of those plants that grew. -61- In the air-dry corn (Table XVI) no germination resulted from the 15 minute heating. PCG corn consistently had a higher, percent of germination, total green weight, average green weight per plant and height per plant, Pox varied widely being high in average green weight per plant and height per plant, but low in germination and total green weight. This was probably due to the fact that Fox fre- quently had a few highly resistant kernels which produced large plant! This is even more noticeable in Table XVII, where, at temperatures which killed practically all the kernels, Fox occasionally sent up a fairly vigorous seedling. The inherent weakness of Fox is shown by its low germination. PCB was high in germination and total green weight but low in average green weight per plant and height per plant In Table XVII we have the reverse of Table XVI. It is an extreme example of the superior resistance to heat of PCB after desiccation. This is shown especially in the percent of germination. An occasion- al resistant kernel, especially in Fox, but also in PCG, sent up a seedling even after severe treatment. PCB shows remarkable germina- tion throughout. The average height per plant was much greater in . PCB and where only those plants that grew are averaged we have: PCB-38.6 cm., Fox-30.5 cm., and PCG-43.0 cm. This same ratio holds in green weight per plant. -62- V . CONCLUSIONS . 1. Air-dry corn, containing 10-11$ moisture is killed by exposure to 80°C and 90°C for 25 and 10 minutes respectively and is in- jured by exposure to 70°, 80° and 90°C for 80, 10 and 5 minutes respectively. 2. Under air-dry conditions, the apparently diseased corn (PCB) con- tains the most moisture, apparently disease-free (PCG) the least moisture and the badly diseased (Fox) an intermediate amount. The resistance to heat is inversely proportional to their moisture content. 3. The resistance of corn to high temperatures varies inversely as its water content at the time of heating. 4. After desiccation over sulphuric acid the apparently diseased corr (PCB) contains the least moisture, apparently disease-free (PCG) the most moisture and the badly diseased (Fox) an intermediate amount. 5. After desiccation the apparently diseased corn (PCB) is very much more resistant to heat; compared with apparently disease-free (PCG) and badly diseased (Fox) corn, than its slightly less moisture content would indicate. This great- er resistance becomes evident only as the temperatures be- come injurious. 6. After desiccation, apparently diseased corn (PCB) is very resist- ant to heat, apparently disease-free (PCG) less resistant, and badly diseased (Fox) is least resistant in spite of its moisture content being less than that of apparently disease-free corn (PCG). This last difference may be ex- plained by the superior vigor of apparently disease-free (PCG) and the diseased weakened condition of badly diseas- ed (Fox) . 7. Desiccation brings about changes in the corn which cause apparent- ly diseased (PCB) to become very resistant to heat and causes badly diseased (Fox) to become less resistant. What these changes are is not known. 8. Desiccation over sulphuric acid in a closed vessel is not uniform being greatest, farthest from the surface of the acid, and least, closest to it. This gradient gradually lessens as the length of desiccation increases. 9. The resistance to heat of air-dry corn, both in the laboratory and out-of-doors, varies with the variations in climatic conditions-humidity. The three kinds of corn tested vary essentially alike. 10. Placing the heated corn in water immediately after treatment has no injurious effect on its viability. . . . - , -63- 11. Germination of heated corn is better in rag dolls than in soil. 12, Growth follows, in general, the degree of viability of the treat- ed and untreated corn. 13. The percent of germination , green weight and height of plants, grown in soil, from heated corn, parallels the behavior shown in germination. In air-dry corn apparently disease- free (PCG) is consistently highest, with apparently diseas- ed (PCB) lowest, and badly diseased (Fox) intermediate. In desiccated corn, apparently diseased (PCB) is consist- ently highest, apparently disease-free (PCG) usually low- est, and badly diseased (Fox) varies between lowest and intermediate . . . * . . . -64- VI o LITERATURE CITED. 1. Atanasof f , D., and Johnson, A. G. Treatment of cereal seeds "by dry heat. Journ. Agric. Research. 13:379-390. Jan. 1920. 2. Branstetter, B. B. Treatment of seed to control root and stalk rots. Ahst. Phytopath. 12:30. 1922. 3. Burgess, J. L. Relation of varying degrees of heat to the via- bility of seeds. Journ. Am. Soc. Agron. 11:118-120. 1919. 4. de Ong , E. R. Effect of excessive sterilization measures on the germination of seeds. Journ. Econ. Ent. 12:343-345. 1919 5. Dickson, J. G. Dry heat treatment for control of cereal seed- borne diseases. Annual Rpt. Director, 1919-1920. Wise. Agric. Expt, Sta. Bull. 323. Dec. 1920. 6. Duddleston, B. H. The modified rag doll and germinatdr box. Purdue University Agric. Exp. Sta. Bull. 236. 1920. 7. Ewart, A. J. On the power of withstanding desiccation in plants. Proc. and Trans. Liverpool Biological Soc. 11:151-159. 1897. 8. Goodwin, W. K. Heat for control of cereal insects. Ohio Agric. Exp. Sta. Bull. 354. 1922. 9. Groves, J. F. A method of prophesying the life duration of seeds Trans. 111. Acad. Sci. 8:133-136. 1915. 10. Groves, J. F. Temperature and life duration of seeds. Bot, Gaz. 63:169-189. 1917. 11. Haber landt, I. Die oberen und unteren Temper aturgrenzen fur die Keimung der wichtigeren Samereien. Landw. Versuchsstation , 17:104-116. 1874. 12. Harrington, George T., and Crocker, William. Resistance of seed to desiccation. Journ. Agric. Research 14:525-532. 1918. 1 1 , 13. Just, L. Wirkung hoherer Temperaturen auf die Keimffa higkeit der Samen. Bot. Zeit. 33:51-52. 1875. 14. Lehenbauer , P. A. Growth of maize seedlings in relation to tem- perature. Phys. Researches 1: no. 5. 247-288. 1914. 15. Montgomery, E. G. Heating seed rooms to destroy insects. Jourr Am, Soc. Agron. 9:105-103. 1917. 16. Waggoner, H. D, The viability of radish seeds (Raphanus sativus L.) as affected by high temperatures and water content. Am. Journ. Bot. 4:299-313. 1917. -65- 17. Walker, J. C. Seed treatment and rainfall in relation to the control of cabbage black-leg. U. S. Dept. Agric. Bull. 1029. 1-27. 1922. 18. White, Jean. The ferments and latent life of resting seeds. Proc. Royal Soc. London, Series B. 81:417-441. 1909. - 66 - VII. VITA. Aaron Raymond Kienholz was born October 18, 1894 near Bellingham, Lac Q,ui Parle County, Minnesota. He received his high school education at Big Stone City, South Dakota, graduating in 1913. He attended North-Western College, Naperville, 111. from 1913-1917 receiving his B. S. degree in 1917. He attended the University of Illinois from 1917-1920, receiving his M. S. degree in Botany in June 1920. He attended summer school, University of Minnesota, Minneapolis, Minn. 1921, He was research assistant in botany, University of Illinois 1917- 18, assistant in botany and plant physiology, University of Illinois 1919-1920, 1920-1921. He was fellow in botany 1921-1922. He was Field Assistant in Blister-Rust Control, TJ. S. Dept, of Agriculture, 3 months in 1917 and 5 months in 1919, and was Assistant, U. S. Forest Service, at Ephriam, Utah, 3 months in 1920. He served 8 months in the U. S. Army 1918-1919, 5 months of this in the A. E. F. France. UNIVERSITY OF ILLINOIS-URBANA 12 108856466