Repository: UIHistories Project: Board of Trustees Minutes - 1880 [PAGE 78]

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76 fibrous bark, aud whose cells are often stored with starch. Contrary to the usual opinion, the cambium, or new layer of thin walled, growing cells just outside of the wood, is by no means the seat of the disease. Often when the whole thickness of the bark perishes, the cambium retains its vitality, and sometimes forms a fresh layer of new bark beneath the old dead coating. In this case the limb or tree may survive without severe, apparent injury. In summer, such a change may take place while the leaves remain green upon the infected branch, showing nothing of their narrow escape from destruction. The wood of a young limb is often discolored above the diseased part by the ascending water colored in its passage through dying and brown portions. The staining is especially noticeable in the fibro-vascular bundles (woody fibers) which turn out into the leaf stalks, and which are the chief water carriers to supply the loss by transpirations from the leaf surfaces. This stained wood may be still healthy in every particular, and continue its proper functions, upon the recovery of the really diseased parts. There is no evidence of the progression of the disease in the wood through which the chief movement of the water on its ascent from the roots to the leaves takes place. The leaves, however, are usually infected from the diseased bark from which they arise. The bacteria work their way through the tissues of the leaf stalk, and spread throughout the parenchyma (soft tissue) of the blade. It is also probable that infection starting in the leaf may spread downward to the stem when conditions are favorable, but infected leaves do sometimes die and fall from their attachments without communication of the malady to the cells of the branches. The dying leaves become smeared, especially during dewy nights, with the exuding bacteria. When dry they form a varnishrlike coating upon the leaf surfaces, in which condition they retain their vitality for an undetermined length of time.

CHEMICAL CHANGES.

My colleague, Professor H. A. Weber, kindly determined for me the kind of fermentation which takes place in the diseased bark. He found, first, that carbon dioxide is abundantly given off. Bark in which the fermentation is active put into water in a stoppered bottle, quickly shows the forming gas. In a few hours the pressure resulting from the accumulating gas forces the frothy liquid out of the bottle in a slow but steady stream. Secondly, butyric acid was determined as a considerable product of the fermentation. This is one of the fatty acids, perhaps best known from its occurrence in butter; it has been heretofore mentioned as one of the products, with carbon dioxide and hydrogen, of a peculiar fermentation of the hydro carbons, such as starch, sugar, various organic acids, etc. It is now well understood that such fermentation is produced by bacteria, either by a special species for each substance, or perhaps one and the same for all of these organic compounds. Cellulose (cell wall substance) also undergoes, when the conditions are favorable, the same kind of fermentation. A brief account of investigations upon these peculiar transformations will directly contribute to