A N SB 608 A lN P4 B8 i 1 Copy i ESSAY ON PEAR-BLIGHT. HEAD BEFORE THE POTOMAC FRUIT-GROWERS' ASSOCIATION, WASHINGTON, D. (J. By JEHU BRAINERD, TOGETHER WITH AN INTRODUCTORY NOTE BY J. P. KIRTLAND, M.D. COLUMBUS: NEVINS & MYERS, BOOK AND JOB PRINTERS. 1876. < u »»*»--»»»< J, z Jvsti&tfjL , COLUMBUS: NEVINS & MYERS, BOOK AND JOB PRINTERS. 1876. •s o^ ^J\ (V PEAR-BLIGHT. [The blight in pear trees is one of those singular phenomena which hitherto has defied successful investigation. The following article, con- tributed by Prof. Brainerd (formerly a professor in the Cleveland Homoeo- pathic College, but during the past fifteen years occupying a very respon- sible and important position in the Patent Office in Washington), is so highly indorsed by Prof. Jared P. Kirtland, of the Cleveland Medical College, as to induce one to believe that if Prof. Brainerd's theory is not absolutely the true one, it is at all events much nearer the truth than any heretofore promulgated. There is at this moment no one in Ohio who is the peer of Prof. Kirt- land in vegetable physiology. During an active intellectual life, which has happily been extended to the full measure of four score years, he has been a vigilant and appreciative observer of every phenomenon of vegeta- ble life which presented itself to him. To his intelligence and skill are we indebted for several of our choicest varieties of cherries, the " Gov. Wood," "Kirtland's Mary," and others. His successful experiments in budding, grafting, inarching, and hybridizing fruits,' flowers, grapes, and berries are almost endless. A theory relating to diseases in the vegeta- ble world must, therefore, have positive merit before it can receive such an affirmative commendation at his hands. — Klippart.] PROF. KIRTLAND'S LETTER ON PEAR-TREE BLIGHT. East Eockport, Ohio, October 28, 1876. Prof. Jehu Brainerd, Washington, D. C. : Dear Sir: I have recently read your interesting and instructive re- port on "The Pear-Tree Blight." Allow me to congratulate you on having probably discovered the origin and nature of that malady, a mal- ady that has hitherto baffled the investigations of the scientific and practical pomologists. A knowledge of the pathology of a disease of the human system is often an important advancement towards effecting a cure or a prevention ; a remark equally applicable to diseases of the vegetable kingdom. In the summer of 1812, while pursuing the study of medicine in Hart- ford, Connecticut, a low and malignant fever appeared and spread ex- tensively in that city. Athletic soldiers in the United States canton- ment, as well as citizens, were frequently one hour apparently in the enjoyment of perfect health, and in the next sinking into the arms of death, perhaps before remedies could be applied. Coincident with the spreading of that epidemic among the human family, blight appeared extensively in the pear orchards. Trees were attacked of all ages, some dating back to provincial times, and of size equaling those occasionally met with at this day on the banks of the Detroit river, the remains of French planting in or before the times of Pontiac. Its attacks were as sudden as those of the sinking fever, and resulted suddenly in either the death of the trees or of extensive impair- ment. Public attention was greatly awakened by its ravages, and as ignorance of its cause prevailed, and in Avant of an explanatory hypoth- esis, the public generally concluded that it was the same pestilence which walketh in darkness that was alike laying its heavy hand on the people and the pear trees. This indefinite hypothesis prevailed for a time, till, in succession, it was displaced by that of insect depredation, frost impres- sion, and fungoid poison. Neither of these suggested any practical means of relief from the evil. Since that period, sixty-four years, I have attentively watched the progress of the blight in different and remote parts of our country, and noted numerous facts bearing on the subject. Your views seem to embrace a well-founded theory of the cause of the disease, which indicates appropriate methods for preventing or counter- acting it. More phenomena attending its rise and progress are thereby explained than by any or all the hypotheses hitherto advanced. I am happy to add that my own experience during that long interval of time, trivial as it may have been, sustains their correctness. If they be cor- rect, of which little doubt can be entertained, it is highly important that they should be extensively diffused among practical pomologists. No specific is at present known, yet evidences are not wanting that an energetic and persevering course of management will do much to remedy the evil of this disorder. The cultivator must take into consideration the character and selection of the variety of the fruit (Seckle and Winter Nellis rarely blight), the soil, and its condition in relation to drainage and moisture, special manures, cultivation or non-cultivation of the ground, shading and protection from the sun and from a south and south- western exposure, mulching, freeing the bodies from old and rough bark, and washing annually with a solution of soda ash, correct pruning of the season's growth in autumn, and pinching off the top of each limb before the formation of the terminal bud, late in June, and other items too numerous to mention. Incidentally, it may be added, that the cultivator should learn to gather his fruits at the moment the stem will cleave from the spur with- out fracture, and to ripen them in a dry room. Each individual winter or autumn pear must be, immediately after gathering, wrapped in a sep- arate paper, as oranges are preserved, and packed not over three layers deep, in either drawers, boxes, or crocks, placed in a dry and empty room. If the rind be allowed to wilt before the wrapping and packing be accom- plished, the fine qualities of the variety will never develop. Bishop Heber wrote that he found none of the East India fruits as palatable as those of temperate Europe. A Baron de Anjou, Dix, Lycur- gus, or Winter Nellis, thus ripened, will favorably compare with the orange, guava, and pine apple of the tropics. Much is yet to be learned in the art and science of pear culture. Very respectfully yours, Jared P. Kirtland. REPORT ON THE BLIGHT OF THE PEAR TREE. » BY PROF. J. BRAINEUD. So far as I am able to learn, there is no settled theory in regard to the cause of the Pear-Tree Blight, and to my mind the discussion of subjects not definitely established accords perfectly with the ruling spirit of this Association, and when they are carefully considered can scarcely fail of some good results. If our extreme modesty forbids the approach of such subjects, may it not be said that we fall short in the first and foremost object for which we are associated ? In order to comprehend the full significance of these observations, it will be necessary to call to mind some facts regarding the structure of plants and trees, and the phenomenon of the circulation of the sap. In what is called saji-wood there is laid up in &tore soluble matter des- tined to contribute to the future development of the tree. This is clearly shown in the sugar-maple (acer saccharinum) , and a knowledge of this fact is made available for obtaining a delicious sweet. Sap is essentially a watery fluid, which the roots absorb from the earth, and contains or holds in solution a minute quantity of carbonic acid and ammonia and a few mineral constituents, drawn from the soil in a con- dition of solution in water. In its ascending course, through the cells of the sap-wood, it meet with and dissolves a portion of the soluble cell-contents, and thus becomes a Read before the Potomac Fruit-Growers' Association, Washington, D. C., September 5, 1876. 6 more and more dense as it approaches the bud where it is appropriated to the development of the leaf, in which it undergoes a futher elaboration, and returns upon the outside of the sap-wood, to form a new growth, and in this condition is called alburnum. In "Rhind's Vegetable Kingdom" this matter of sap circulation is fully examined. In this and other standard works on botany the fact that the ascending sap in exogenous trees passes upward through the growth of the previous years (hence called the sap-wood) is so universally admitted that its discussion here would be out of place. The alburnum, then, is the layer or growth of the present year, that will form the sap-wood of the succeeding year. And this sap-wood may continue in activity for a number of years, and until the cells which form its structure become filled with mineral deposits, thereby becoming heart- wood and of no further use, so far as the vitality of the tree is concerned. It is, however, of value in giving strength to sustain the accumulating weight of the growth, but the vitality of the tree would not be affected by its removal. Before I call attention to the sketches I have made, from microscopic examinations of the specimens submitted for that purpose at the August meeting, and since procured, it will be proper to examine, briefly, the anatomy of the growth under consideration. The sap-wood is made up essentially of elongated cells, either joined end to end, or overlapping each other. During the growing season these cells are filled with crude sap of constantly increasing density from the spongiole of the root, where it is little else than water, to the extremity of the highest leaf. In the leaf system it becomes elaborated sap, fitted for the formation, in its descent, of a system of new cells between the bark and the last year's growth, and which, when in the act of forming, is called alburnum, as before stated. It is owing to the extreme delicacy and tenderness of these forming cells in the spring of the year that we, in our boyhood days, were enabled to make our "toy whistle of bark." I will now call your attention to the possible causes of blight, and pro- ceed to examine the sketches I have made from actual views under the microscope. In an English work on " Practical and Scientific Fruit Culture, by Charles R. Baker," pages 420, 421 , we find this significant statement : " That the enlargement of the flesh of a fruit, the entire or partial absence of seeds, are the result of disease, strictly considered; and yet these conditions are very desirable in fruit culture." What we are to understand by the term disease, in this statement, must be held to relate wholly to the vitality of the tree, for it is a well-known fact that in fruits, as well as in animals, an excessive development in any particular direction — the fostering of favorite qualities — weakens the power of resistance against the vicissitudes of climate and the nu- merous natural foes to longevity, producing what may properly be termed an ancemic condition of the tree. Fig. l. NATURAL SIZE— SOUND BRANCH, AND SAME BLIGHTED. When I entered upon this examination, I was inclined to attribute the blight to the depredations of some species of insects, but I determined to conduct the investigation without bias ; I could not, however, pass over this point without due consideration. 8 I therefore made diligent search for evidences of this character, but found none, with the exception of two or three spurs in perhaps fifty ex- amined, in which appeared slight evidences of the work of the Pear- Blight Beetle, Scolytus pyri. This insect, which is very small, causes a blight of spurs and small twigs, which, in its outward appearance, resem- bles the common pear-tree blight. The limbs or spurs attacked turn black and die, while other parts of the tree remain healthy. The egg of the insect is laid in the axil of the bud; the larva eats its way inward through the alburnum, and forms a circular passage in the sap-wood, thus cutting off the vessels for the as- cending sap; the whole part above, being deprived of nutriment, dies. I am satisfied, from a most careful examination, that the kind of blight under investigation is not caused by this nor any other insect, for I failed to find either the grub or the conditions above stated. Since writing the foregoing paragraph, I have succeeded in finding the living larva of two individual specimens of Scolytus pyri. The branches NATURAL SIZE — LARVAE OF THE SCOLYTUS PYRI, MAGNIFIED TWENTY DIAMETERS. had been in my possession about ten or twelve days. At this stage of their development their length is about one-tenth of an inch, a reddish brown head, two short hooked mandibles, dark eyes, large thorax, fifteen articulations, two or three stiff hairs upon the sides at each articulation, body very light straw color, almost white, and semi-transparent. The point where the larva entered the bark is scarcely perceptible without a magnifying glass, appearing not larger than a puncture made with the point of a needle. Their course is first inward, toward the pith from the base of the spurs, thence downward along that soft tissue. The discovery of these living larva should not be taken as evidence of a cause of the blight, inasmuch as their development was subsequent to the blight. That the egg of the insect was deposited previously to, or about the time of the occurrence of, the blight is quite probable, but the tree had sustained no injury from the larva at that time. We must, therefore, look for other causes, and in doing this we can have no more reliable guide than the revelations of the microscope. I next turned my attention to the discovery, if possible, of a fungoid growth, by many regarded as the cause of blight. But, upon the closest 9 scrutiny, no evidence of this character appeared. I am, therefore, forced to the conclusion that fungus, whenever it does appear, is the consequence, and not the cause, of blight. Fig. 2. Fig. 3. a. Pith. b. Sap-wood. c. Alburnum. NOT BLIGHTED. BLIGHTED BRANCH. ' (Both magnified two diameters.) I now call your attention to the microscopic views which I have pre- pared with scrupulous fidelity to the specimens before me. Figure 1 shows a healthy and a blighted branch. Figure 2 shows cross and longitudinal sections of the healthy branch magnified. Figure 3 shows a like view from a blighted branch. Figure 4 shows a slightly magnified branch blighted twenty-four hours previous to examination. The entire growth above the blighted portion was green and vigorous, showing a continuous supply of ascending sajj, while the bark and alburnum in the blighted portion was dark and with- ered. Figure -5 shows magnified vertical sections of health}' and blighted branches. Figure 6 shows magnified views of stomata, in the green bark of the young shoot, both natural and blighted, with cross-section of the same. In these examinations but one conclusion can be entertained, and that is, that the newty formed cells in the alburnum have, from some cause, been ruptured, and the elaborated sap, destined for the support of the fruit and the perfecting of the new growth of wood, poured out into the interspaces of the cells, coagulated and disorganized, producing in the 10 vegetable tissue a condition analagous to what is termed extravasation of blood in the animal tissue. A comparison of the healthy alburnum with that struck with the blight shows most clearly that this statement is fully borne out by the facts in the case. The microscopic appearance of the coagulated sap in the blighted por- tions of the stem, under a high magnifying power, was most remarkable. Every vestige of cell formation was destroyed, and nothing could be seen but a dark coagulated mass, pushed out in rough masses through fissures in the bark ; and this appearance extended through the whole thickness of the alburnum, while the sap-wood remained in a perfectly healthy state, conveying sap to the unblighted portions above, as seen in figure 4. The color of this coagulated sap presented all shades, from a pearly luster to a dark brown, presenting many irregularities and cav- ities, caused by contraction from loss of watery fluid. The external bark and leaves appeared as though they had been scorched in a fire; hence the disease is aptly called " Fire Blight." There are two causes that produce the rupture and destruction of newly formed cells in the alburnum, and the action is very sudden and certain. These are extremes of heat and cold. In the spring of 1875, in Ohio and along the lake shore fruit region, after the trees had put forth their leaves, a sudden fall of temperature from summer heat to twelve or fifteen degrees below freezing killed outright nearly every pear tree in that ex- tensive fruit district. I examined many trees soon thereafter, and found the external ap- pearances exactly similar to what is called the " Fire Blight;" that is, the trees had the appearance of having been roasted in an oven. The green and tender portions of the tree, especially the alburnum, are made up of cells whose membranous walls are very thin and delicate, and when the sap with which these cells are always filled is subjected to sudden expansion, from either high or low temperature, the cell-walls become ruptured, and the sap, of course, runs out and is diffused among the tissues, and its nutritive action is lost. A putrefactive condition soon follows, giving rise to fungoid growth, if other conditions are favorable. In order to test thoroughly the influence of heat, I subjected a vigorous and healthy branch of a pear tree to an artificial heat of 108 degrees Fah. for twenty minutes. The effect upon the leaves and soft tissues was ex- actly like that of the natural blight. The normal heat for the fruit-producing season ranges from 65 degrees to 85 degrees Fah., the mean of which is 70 degrees. 11 A temperature of 95 degrees is dangerous, and 100 degrees to 108 degrees is disastrous. Fig. 4. /^