PEAR BLIGHT.

The destructive agency known as the pear blight has occasioned much anxiety among the growers of this delicious fruit, and discouraged the small farmer from attempting its cultivation.

The New York experiment station has given it attention, and Prof. J. C. Arthur, the botanist of the institution, has reported the results of his investigations and experiments:

"Among the numerous experiments relating to the diseases of plants which have been performed at the station, those on pear blight have excited the most interest. The first case of blight noticed in this vicinity was on a pear-tree in a neighbor's yard, July 11, 1884, and on July 26 a small branch of quince in the station garden was found blighted. These were both promptly destroyed. No other case of spontaneous occurrence of the disease has been observed within a mile or more of the station. It has, however, appeared in considerable virulence among the pears and quinces in some localities in this region.

This seemed a most favorable opportunity of investigating the infectious nature of the disease, and, accordingly, on July 16, a pear orchard was visited, and some of the diseased branches secured. Among these was one with viscid, yellowish drops exuding from the stem. With a needle a puncture was made about an inch from the extremity of several branches of a pear-tree in the garden, and a very little of this excretion inserted. It was applied in the same manner to some terminal leaves, but a difficulty in manipulation rendered the result doubtful, for the excretion being very sticky, and the leaf thin, it was not easy to remove it from the needle and insure its remaining in the wound. In from six to eight days every branch inoculated showed unmistakable signs of the blight. The bark turned brown and then blackish about the puncture, the color extending gradually through the stem, passing upwards toward the end of the branch much faster than downwards or around the branch. On the ninth day most of the wounds exuded some of the same viscid fluid which was used in the first place. They were all removed on the thirteenth day to prevent the disease securing any permanent hold on the tree. Most of the infected

branches were blackened for a foot or more, and all the tender young leaves as well, all being thoroughly dead. It was noticeable that the full grown leaves were rarely affected, and mostly remained green up to the time of the removal of the branch. Only one of the inoculated leaves became infected, and this was a young, tender one. The disease spread to the stem, and worked the same as in the other cases.

At the same time a portion of the same virus was applied to two young apple branches. Both showed the disease in eight days. It spread gradually, until, on the thirteenth day, about two inches from the apex was quite dead and dry, and the branches were removed.

On July 24 an inch or so of diseased pear stem was sliced up in a watch glass half full of water, and after stirring about, the chips were all removed, which left the water slightly milky. This was used to inoculate with by making a puncture with a pin, and adding a small drop from the watch glass. It was applied to the branches of several kinds of fruit, but sufficient time has not elapsed at this writing to show results, except in the case of a very young branch of June berry (Amelanchier Canadensis) about six inches long, which showed unmistakable signs of blight on the sixth day. But the most remarkable results yet secured were gotten by inoculating the fruit of the Bartlett pear with this watery infusion. On the sixth day they were all blackened for some distance around the point of inoculation, and exuding a copious flow of yellowish fluid, which ran down the side and dropped on the ground. In fact, each was a great running sore. Upon cutting open the pears, they were found to be discolored almost throughout their interior. Inoculation at the same time on quince fruits showed the disease in seven days, but without any exudation, and upon cutting them open, only about one fourth of the interior was affected.

We may make the following general statements, which the experiments so far tried (some sixty in all) fully sustain. The disease known as pear blight is infectious, and may be transmitted from one tree to another by inoculation. It is not confined to the pear, but may attack other pomaceous fruits, as the apple, quince, English hawthorne, and June berry. It is more

active, and progresses most rapidly upon young and succulent portions of the tree.

Under the microscope any bit of diseased tissue shows inconceivable myriads of minute bacteria which fill the water of the slide in which it is mounted like a cloud. It is, therefore, not necessary to depend on external appearances in order to determine the progress of the disease in a branch, for the microscope will decide with absolute certainty. There cannot be a rational

doubt that the bacteria are the cause of the disease."

This has been regarded as a new disease, and has been so announced. The attention of fruit-growers and scientific investigators has been called to it, but they have been slow in expressing an opinion regarding it, and slower still in prescribing a remedy. In a volume of the old N. E. Farmer, published by John B. Russell in 1829, and edited by Thomas G. Fessenden, is a letter to the editor, from New Jersey, which refers to a blight very similar to that which affects the pear of to-day, and it appears to be identical with it. The editor does not endorse the doctrine of the author, neither does he assent to the theory which the New Jersey gentleman attacks. We publish the paper in full, with the conviction that it will be read with interest by all fruit-growers:

"What Mr. Buel says of the fire-blight is not so conclusive to my apprehension as are his remarks on the girdling protuberances which have hitherto been so destructive to the plum and Morello cherry. He is not alone in attributing the disease called fire-blight to the venom ejected from an insect; but, much as I should like to see this doctrine established, I cannot admit it for a moment. I am fully aware that a single drop of poison introduced into the animal system will decompose the fluids and cause death, whether it be injected by a rabid animal or by an enraged reptile. And I have no doubt but that if a sufficient quantity could be forced into the circulation of a plant, that the whole mass would be rendered unfit for the uses to which the sap is destined. I have made various experiments on the young and old branches of pear-trees, but although I used the different poisons in a concentrated and diluted form, such as prussic acid, nitric acid, muriatic, &c., as well as croton oil and mercury, in several forms, and although I sacrificed many an insect

such as poisonous spiders, &c., yet I never succeeded in injuring the tree farther than an inch or two above and below the puncture. We know that the rupture of a blood vessel, by a determination of blood to the head, will cause instant death in man, and that this is often effected by external influence, such as exposure to the sun. Here is an analogous case as it respects loss of vital principle, and the cases approach as nearly as the nature of animal and vegetable life can approximate.

An exotic pear, such as the Vergalouse, the Beurré, the St. Germain, or the D'Auche, grows very luxuriantly in our climate. They have the capacity of attracting a greater quantity of fluid nutriment than those trees which are indigenous. The fireblight occurs more frequently after a summer shower in July or August, and during the sunshine. A shower falling on any plant while the sun shines fiercely is always more or less injurious. It has been my object for many years to ascertain the cause of this destructive disease; but vigilant as I have been, and still am, I have never yet detected any insect in the act of puncturing the tree so as to cause fire-blight, although I have actually seen the end of a limb perish with fire-blight before my eyes while examining it. I once stood under the shade of a fine St. Germain while I was directing my gardener how to amputate the limb of a similar tree which stood about ten feet from me. I discovered the blight immediately after one of those hot showers, and, as is my constant practice, I hastened to the tree that the injured limb might be instantly separated. Whilst I stood under the St. Germain before mentioned, my eye rested on the horizontal branch before me, and to my surprise I saw the leaves change color from a dingy yellow to a dark brown! I had the limb cut off far below the blight, and saved the tree, as I did the one opposite to me.

We all know that the blood of animals undergoes a change as soon as it comes in contact with the atmosphere. It not only becomes altered in its nature, but it coagulates. The introduction of atmospheric gases produces this result. So likewise with respect to the albumen or white of an egg. The substance certainly is completely changed by the mere presence of heat, but what new principle of matter is gained by the operation is and will be forever unknown. While the sap of plants is con

fined within the proper vessels, it possesses the healthful qualities necessary to it; but if a rupture takes place at the tender extremities of a limb, or should no rupture occur, but merely a detention or congestion of sap be the consequence of the powerful rarification which the hot, moist atmosphere causes, the sap, by coming and remaining more immediately in contact with external gases, will acquire deleterious qualities wholly unfit for the uses of the plant. Every compound fluid undergoes a marked change when exposed to the air. Crystals become deliquescent, and fluids are crystallized according to the amount of chemical agents which are present in the atmosphere. If the sap of plants, by the detention of its particles at the extremities, becomes glutinous, or acrid, or otherwise vitiated, the returning vessels are no longer suited to receive it.

Perhaps the tender and extremely delicate ligaments which unite the different vessels are decomposed by the acrid principle which the descending sap has acquired. Certain it is that the parts which are overflowed by the vitiated sap have the appearance of being excoriated. Owing to our imperfect knowledge of the structure of plants, we cannot ascertain whether any of the vessels be ruptured, as in cases of congestion in the animal system, or whether any of the adhesive membranes be decomposed. If we macerate the back and leaves of a blighted limb in water for six hours, and likewise macerate the bark and leaves of a healthy limb for the same space of time, we shall find that the acrid principle is more active and in greater abundance in the water in which the diseased parts were immersed than in the other. There is therefore an excess of acid in the virus which excoriates the inner surface of the bark. A concentrated acid seems to be the base of all poisons, but they do not all necessarily emanate from the animal creation, whether dog, snake, or insect.

We rely much on the instinct of inferior animals and insects for our safety. A rabid animal inflicts a wound, not from instinct, but from the absence of all sagacious sensation. He is in the delirium of fever. Not so with a snake or spider. It is the instinct of self-preservation, self-defence, or revenge which prompts them to inflict a wound. The instinct of animals, including all that have locomotive powers, is seldom at fault in