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MICROSCOPIC RESEARCHES:

Resulting in the discovery of what appears to be the cause of the so-called

Blight in Apple, Pear and Quince Trees; and the Decay in their Fruit, déc.

BY J. H. SALISBURY, M.D., AND C. B. SALISBURY.

Commencement and Progress. During the summer of 1862 the blight began to affect the apple, pear and quince trees in Central Ohio, about the 12th of June. It made its appearance suddenly, after warm moist weather. Its invasion and progress was identical with the attack of blight which was so destructive to apple, pear and quince trees in 1847 and '48, throughout the Northern and Eastern States. At different elevations, the trees were affected in different degrees. Generally on, and, for a short distance, above the third terrace from the stream bottoms-which corresponds with the line of suspended stationary vapors and fogs—the trees were much more affected than at higher or lower levels.* Some trees in an orchard would be affected much more than others adjacent on the same level. Often the more thrifty trees and most vigorous sprouts, would be the ones the most invaded. Sometimes twigs and limbs would commence dying at their extremities, and this death would gradually advance towards the base of the limb, always advancing faster in the layer of new soft wood and bark (cambium) than in the more solid beart wood. At other times the death would commence in the middle of a limb- often several feet from its extremity-killing the new wood and bark first, and grad. ually advance from the point of starting, up and down the limb, leaving the heart wood sufficiently alive to communicate, for weeks, sap enough past the diseased and dead surface rim, to support the vitality of the ex. tremity. In other instances, a surface-patch, merely, on the side of the limb, would die. This disease progressed till about the first of August, when its advance seemed to be checked by the tissues of the young wood becoming too firm for the further invasion of the fungus.

* In our examination of rich peaty, wet low grounds and bogs, with the view of determining the character of the malarious matters produced by them and elevated in the fogs and night vapors rising therefrom, we found the fungus, which is the cause of the apple, pear and quince blight, &c., growing luxuriantly on and in the peculiar, palmelloid, algoid growths, that are so prolific upon the broken-up sod and surface of rich bogs. (These palmelloid growths, with their parasitic fungus, will be fully described in a paper, which will soon be ready, on the Cause of Intermittent Fevers, &c.) The occurrence of the apple, pear and quince tree blightfungus, so abundantly in positions where their spores are liable to be elevated in every rising fog or night vapor, and the further fact, that trees are more affected with blight along the line of elevation described by the stationary night and morning vapors, points strongly to the bogas grounds as one source of this destructire fungus.

In our office yard were several apple trees affected with the blight. We selected several limbs for observation, which began to die near where the spring's growth commenced. These limbs were first affected between the 12th and 15th of June. Death gradually advanced both towards the base and extremities of the limbs, till on July 14th the limbs were all dead to their extremities. July 15th, cut off the limbs for dissection and microscopic examination. Found the entire limbs, through and through, at the point where the blight commenced, filled with the mycelium of a peculiar fungus. The threads wound around in every direction among the woody cells; and where there were intercellular spaces, these were filled with the moniliform threads, fig. 3, Lignograph A.* In passing up or down the limbs, the same appearance was presented, save that the fungus was more and more confined to the new layer of wood as you departed from the point of attack. For several inches beyond (in the tender, rapidly growing twigs), where the limbs were not actually dead, dead lines, the size of a knitting-kneedle, extended in the soft viscid, gelatinous matter (cambium), which was to form the new annual layers of wood and bark. Along these dead lines could be traced the moniliform threads, making their way among the cells.

Fig. 1, Lignograph B, represents a portion of a transverse section of the limb of an apple tree, affected with blight. This section was taken about

inch from the live portion. It will be seen that here the young plants are making rapid headway among the cells. In the center of this slice is an intercellular space, filled with short moniliform threads.

Figs. 3 and 5, Lignograph C, represents a portion of the moniliform filaments in a part of the limb that had been dead since June 15. This portion of the branch was much shrunken; and in the intercellular spaces and between the cells, occur these moniliform (mycelium) threads, winding about and knit together in various ways.

Fig. 6, Lignograph D, a longitudinal section of wood immediately beneath the bark; showing short moniliform threads in the interstices between the vessels.

Figs. 2, 4 and 7 (Lignographs B, C and D), fungoid filaments found in a single intercellular space of the wood of a dead twig. Fig. 4 represents the same species as figs. 3, 5 and 6. Figs. 2 and 7 represent fungi that we have found only in portions of twigs that have been some three weeks or

* The Lignographs or engravings will be found on pages 473 to 479.

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more dead. They are probably the consequence instead of the cause of the disease—being developed only from dead and decaying tissues. Fig. 1 is very peculiar, from the fact, that each cell sends off lateral hairs, giving it a barbed appearance. This fungus occurs in tufts in the interstices of the wood that has been dead for three or four weeks, and is accompanied, so far as we have seer, with the fungus represented by fig 2, Lignograph B.

In the blighted quince twigs are found the same moniliform threads seen at figs. 3, 4, 5 and 6, and a fungus that resembles fig. 2, in the apple. The blight produced most of its ravages, in its attacks on the trees, from the 12th of June to the 15th of July. From the 15th of July to the 1st of August, its progress was slight. From the 1st of August forward, the trees improved. The fruit was attacked first when about the size of a hazel-nut, destroying much of it. It was again attacked when about half grown; and, finally, again as the fruit was maturing, destroying a large portion of the crop. DESCRIPTION OF THE APPLE, PEAR AND QUINCE BLIGHT FUNGUS.

(Sphaerotheca Pyrus, Salisb.) It would seem highly probable to those who had not carefully explored the field, that the fungus (S. Pyrus) which causes the blight in the apple, pear and quince trees, &c., might with propriety be arranged under two different and well marked species. A careful investigation of the subject, however, affords satisfactory evidence that these variations are only the different stages in the development of the same species, modified perhaps somewhat by the varying states of the bodies on which it grows, and the varying meteorological conditions to which it is subject at different periods of the season. As long as the tissues, in and on which it grows, continue soft and tender, and filled with nutritive juices, it appears to have a tendency to be developed in the form and to produce the kind of fertile threads seen at figs. 13 and 20, Lignographs E and F, and figs. 35, 38, 39 and 48, Lignographs G, H and I. These threads emanate usually from discs or perithecia, like those seen at figs. 29, 34, 45, 46 and 47, Lignographs K, L, M, N, 0. This is the form which is presented when the plant is developed upon the rich, juicy, decaying fruits. After the fruit is somewhat advanced in decay, or becomes dry, and in the twigs and leaves after their cambium and parenchyma begin to harden, and the nutritive juices are diminished, the filaments pass to another stage of development, seen at figs. 24, 25, 40, 41, 42 and 43, Lignograpbs P, G, Q. The fertile threads and the lines and masses of spores, in size, shape and arrangment, assume quite a different appearance from those produced when the tissues

are succulent, soft, and abundantly supplied with nutritive materials. It is thus seen to have two different and well marked modes of fruiting, and several different forms of sporidia. (Figs. 24, 40, 41, 43 and 48 to 58, Lignographs P. Q, N, I, O, R.)

This plant is strictly a parisitic fungus, that affects organic tissues; and appears to be poisonous both to plants and animals. Its sporidia are often inhaled in large quantities during its period of rapid reproductive development; and frequently the expectorated sporidia are found vegetating. That the inhaled sporidia produce more or less irritation of the pulmonary mucous membrane is quite probable, from the fact that in walking over rich boggy grounds, where the surface is more or less broken, exposing the fresh peaty soil, especially during the months of June, July, August and September; or in passing, in the morning or evening, over positions where hang the vapors from boggy localities, the fauces, throat, and pulmonary membrane becomes dry, feverish and congested, which lasts often for hours after removal from continued contact with the exciting cause; and from the further fact that the expectorated mucus, after leaving such localities, is found filled with the sporidia of this fungus.

This fungus belongs to the group Ascomycetes, to the order Prisporia-, cei, and the genus Sphærotheca; for a description of which, see the paper on the Cause of the Blister and Curl in Peach Leaves, &c. This species resembles, and may be found to belong to the peach furgus (S. Persica); but as there appears, at this stage of the investigation, to be specific differences, and not finding it within our range of reading described, we name it after the generic name of the family of plants it so much affects—the S. Pyrus.

This fungus resembles, somewhat, species arranged under the genera Sporochisma and Bloxamia, wbich belong to the group Coniomycetes, and the order Phragmotrichium. There are, however, many marked peculiarities about this plant that separate it from those of the Coniomycetous, and unite it with those of the Ascomycetous group.

One species of Sporochisma, the S. Spilocaea, affects apples, forming the black specks on their surface, which are occasionally so numerous as to make them unsalable. In producing blight, the sporidia begin to develop in the soft, viscid layer of cambium, and follows the vessels up and down from the point of starting. As fast as the mycelium progresses, death ensues. Figs. 14 and 20, Lignographs E and F, and figs. 24, 25, 29, 34, 35, 42, 43, 45, 46 and 47, Lignographs P, G, K, L, Q, M, O and N, represent the usual forms presented by this fungus at different stages. The fertile threads and lines and masses of spores seen at figs. 24, 25, 40, 43, &c., Lignographs, P, G, &c., appear on the dead leaves and twigs, like a

fine dark brown or black carbonized dust. So imperceptible is it that it is with difficulty discovered to be a plant at all. Wherever the mycelium and fertile threads appear, the tissues die, and become carbonized and black; especially is this the case with leaves. Figs. 29 and 30, Lignograph K, represent an early stage in the development of the fertile threads from the discs or perithecia.

The various forms and groupings of sporidia are represented at figs. 20 and 21, Lignograph F, and figs. 24, 25, 26, 27, 28, 31, 32, 40, 41, 42, 43, and from 48 to 58, Lignographs P, G, K, Q, J, N. O and R.

Fig. 32 represents a paraphysis bearing upon its summit spores.
Fig. 24 b, represent young asci.

Figs. 38 and 39 represent portions of the fertile filaments of the plant, seen at fig. 24.

Fig. 11, Lignograph E, represents the mycelium of the fungus, as it appears in the cambium of the limbs which it attacks. Decay follows close on the advance of the mycelium, which runs along in lines in the direction of the new woody fiberg.

Figs. 8, 9, 10, 12, 13, 14, Lignographs S and E, and fig. 42 t, Lignograph Q, represent most of the forms of fertile threads on the branches. Occasionally fertile moniliform lines of spores, like those seen at figs. 8 and 14, Lignographs S and E, may be seen on them and the tender leaves in June and July, during the rapid deposit of woody matter and the abundant supply of nutritive juices.

Fig. 8, Lignograph S, and figs. 40 and 41, and k, 1 and e, fig. 42, Lignograph E, represent masses and lines of sporidia, which are developed either on or in the course of the fertile threads. The mass, fig. 41, is vegetating.

Fig. 42 represents the mycelium and fertile threads of the S. Pyrus, from a branch of a quince tree; and fig. 40, 41, 43, and t, fig. 42, the fertile threads running into lines and masses of sporidia. Figs. 45, 46 and 47, Lignographs M, N and 0, represent the appearance of the discs or Perithecia, under the cuticle, from which emanate the fertile threads, and the various forms of sporidia, figs. 48, 49, 50, 51, 52, 55 and 58, Lignographs J, N and R. The other forms and arrangements of spores are seen at figs. 53, 54, 56 and 57. The spores, 40, 41 and 43, and d, e, g, h, i, k and 1, fig. 42, are produced on the fertile threads, above the surface, and which are believed to be connected directly with the mycelium, without the intermediate Perithaceia, figs. 45, 46 and 47. In the Perithaceia, the formation of fertile threads and asci and sporidia, commences at the center and most depressed portion, as seen at fig. 46, and gradually fill up and occupy the whole concavity with fertile threads. In the perithecium (fig. 47) no fertile threads are yet seen protruding above the lid. Fig. 42 f, are elongated, oval sporidia; m, m, m, fig. 42, are a class of yellowish, quite

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