. Fungous diseases of plants : with chapters on physiology, culture methods and technique . Fungi in agriculture. u6 FUNGOUS DISEASES OF PLANTS. Fig. 28. Crown Gall of Peach the newly formed parenchyma. The centers of these growths ulti- mately become most curiously twisted nodules of tracheides and woody ; Galls upon relatively small roots may not attain more than a centimeter in diameter, while ordinarily on nursery stock, raspberries, etc., they may be as large as a walnut (Fig. 28). On the crowns of large trees they may be much larger. Cross-inoculation experiments. It has cost
. Fungous diseases of plants : with chapters on physiology, culture methods and technique . Fungi in agriculture. u6 FUNGOUS DISEASES OF PLANTS. Fig. 28. Crown Gall of Peach the newly formed parenchyma. The centers of these growths ulti- mately become most curiously twisted nodules of tracheides and woody ; Galls upon relatively small roots may not attain more than a centimeter in diameter, while ordinarily on nursery stock, raspberries, etc., they may be as large as a walnut (Fig. 28). On the crowns of large trees they may be much larger. Cross-inoculation experiments. It has cost no small amount of effort to determine the cause of crown gall. Tourney found a Myxomycete developing occa- sionally upon the cut surfaces of galls in impure cultures. He further observed appearances of the protoplasm in certain cells of the parenchyma of young galls suggesting stages in the development of the plasmodia. The evi- dence was not strong, however, and many pathologists reserved a final opinion regarding the nature of this disease. It was long apparent that the disease is infectious, and many experiments demonstrated that it could be conveyed from one susceptible plant to another by inoculation of the roots with macerated galls or by burying infected parts of diseased plants in the vicinity of healthy roots. The results of rather recent and extensive inocula- tion experiments by Hedgcock are summarized by him as follows : " The soft galls from the almond, apricot, blackberry, cherry, peach, plum, prune, and raspberry have been transferred easily to seedlings of the almond, apricot, peach, and raspberry; less readily to those of the blackberry, cherry, plum, prune, and pear; and with great difficulty to seedlings of the apple, chestnut, wal- nut, and rose. " The soft galls of the apple, chestnut, walnut, rose, and pear, as a rule, have not been transferred readily to any of the plants mentioned. Evidence has been obtained of a wide range of suscep- tibilit
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