. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. REACTION OF THE PLANT. *X'"lG. 26 laled by needl Plant inoculat 90 In many instances there is no perceptible evidence of defense or tissue-reaction in any part of the host, i. e., the attacked plant succumbs quickly, offering no apparent obstacle to the advance of the bacteria. This is true of various soft rots, in virulent forms of pear-blight, in brown rot of young tobacco plants and tomato plants, and in the wilt of cucumbers. In less virulent forms of disease the plant often reacts by building a more or less imper
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. REACTION OF THE PLANT. *X'"lG. 26 laled by needl Plant inoculat 90 In many instances there is no perceptible evidence of defense or tissue-reaction in any part of the host, i. e., the attacked plant succumbs quickly, offering no apparent obstacle to the advance of the bacteria. This is true of various soft rots, in virulent forms of pear-blight, in brown rot of young tobacco plants and tomato plants, and in the wilt of cucumbers. In less virulent forms of disease the plant often reacts by building a more or less impervious wall around the diseased parts, between them and the sound tissues, and thus "corks out" the intruder, e. g., potato-tubers attacked by Bacillus phytoplithorus, various leaf-spots, and cankers. In some instances the presence of bacteria in the tissues leads to the premature develop- ment of organs—blossoms and side branches in the scjuash, inale inflorescence in sweet corn, clusters of roots from other roots in hairy root of apple, aerial roots on tomato, daisy (fig. 26), and tobacco; in other cases retardation of development and atrophy occur. HYPERPLASIAS. In certain types of disease there is a very pronounced reaction of the host. This is manifested by rapid cell- division and enorinous increase in the volume of tissues,the result being a tubercle or tumor which may continue to grow for months (plates 8 and 9) and exceptionally reach a diameter of a decimeter or more. The lowest stages of this hyperplasia may be seen in cankers of various sorts and in the effect of non-virulent cultures of Bad. solana- ccariim on potatoes and tomatoes (fig. 27). The most striking examples are the crown-galls of peach, hop, daisy, sugar-beet, etc. (figs. 28, 29). These enormous swellings are the result of repeated cell-division under the stimulus of the presence of the micro-organisms in the tissues and as already stated inside of the rapidly dividing cells. Just what this s
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