24 PLANT DISEASiES AND FUNGI. 



instance, which is adduced, of the analogy above alluded to : " The 

 likenesses between the inflammations in plants and in animals are 

 best shown in their visible structural changes, and these have been 

 admirably traced by Waldenburg. He has applied various irritants 

 to leaves, fruits, and stems, such as foreign bodies, setons, crushings, 

 cauteries, and others. The results, speaking very generally, are that, 

 as in ordinary wounds, the cell structures actually involved in the 

 injury perish and dry up ; that those most nearly adjacent suffer 

 degeneration, indicated by their protoplasmic contents becoming 

 turbid, and their chlorophyll becoming yellowish or brownish, while 

 in those next to them, and within distances varying according to the 

 injury and the texture of the part injured, enlargement of cells 

 ensues, and increase by division and thickening of the cell walls. 

 In these changes you may study, with comparatively easy experi- 

 ments, imitations (as near as differences of texture will allow) of the 

 most constant constituents of inflammation in animals, especially 

 those of the least acute of the productive interstitial inflammations, 

 leading to thickening, opacity, induration, and other such changes." 

 Pursuing this subject of analogy still further, we come face to 

 face with the results of some of the most recent investigations in 

 which microbes play an important part. It is only very recently 

 that a long entertained suspicion has been verified of the presence 

 of bacteria in plant disease, as well as in that of animals. The 

 disease known in the United States as " Peach yellows " has con- 

 stantly evaded all search for mycelium, or trace of fungoid develop- 

 ment, and yet it is a destructive and insidious foe. Professor Burrill 

 made investigations in 1888 and 1889, but without any decided 

 results. Nevertheless he reports that " he had found in the tissues 

 of the root, and of the old and young stems of diseased trees, an 

 organism, classed with the bacteria, which is not known to occur 

 elsewhere. This organism has been frequently obtained by method 

 of cultures under circumstances which preclude the possibility of its 

 coming from anything except the inner cells of the tree. He had it 

 growing in artificial media, and it exhibited all the peculiarities of a 

 pathogenic rather than a saprophytic microbe. It had peculiarities 

 which served to distinguish it from all others of its kind, and he 

 was convinced it had never before been described by any one. He 

 found it in every set of specimens examined, known to be affected 

 with this disease, and had thoroughly tried in the same manner to 

 find it in healthy stock and failed." Still further he says : " If the 



