36 THE FUNGI WHICH CAUSE PLANT DISEASE 



occurs at 0°. Milk, bouillon, dextrose peptone water with calcium 

 carbonate are the best media for long continued growth. 



The following are recommended as quick tests for differential 

 purposes. Time of appearance of colonies on +15 agar plates 

 made from the tumors; young agar stroke cultures; behavior in 

 milk and litmus milk; growth on potato; behavior in Cohn's 

 solution; stringy ring and suspended filaments in peptonized beef 

 bouillon; inoculations into young, rapidly growing daisy shoots 

 or into growing sugar-beet roots. , 



The organism is readily plated from young sound galls, i. e., 

 those not fissured or decayed. 



In galls on the Paris daisy (Chrysanthemum frutescens) these 

 bacteria were found in small numbers. By plating they were 

 obtained in pure culture and puncture inoculations repeatedly 

 resulted in the characteristic gall. From these the organism was 

 reisolated and the disease again produced, thus giving conclusive 

 evidence that the organism is the actual cause of the gall. Swell- 

 ings began four or five days after inoculation and in a month they 

 were well developed though they continued to enlarge for several 

 months, reaching a size of 2-5 cm. in diameter. 



Tumor-producing Schizomycetes have also been isolated from 

 over-growths on plants belonging to many widely separated 

 famiUes (Compositae to Salicacese). Natural galls have been 

 studied on Chrysanthemum, peach, apple, rose, quince, honey- 

 suckle, Arbutus, cotton, poplar, chestnut, alfalfa, grape, hop, beet, 

 salsify, turnip, parsnip, lettuce, and willow. The organisms from 

 these sources are closely alike on various culture media, and many 

 of them are readily cross-inoculable, e. g., daisy to peach, radish, 

 grape, sugar-beet, hop; peach to daisy, apple. Pelargonium, 

 sugar-beet, poplar; hop to daisy, tomato, sugar-beet; grape to 

 almond, sugar-beet; poplar to cactus, oleander, sugar-beet; willow 

 to daisy. With eight of these organisms tumors have been pro- 

 duced on sound specimens of the species from which obtained. 

 Some cross-inoculate more readily than others, and there are also 

 slight cultural differences. Thus, it is probable that there are 

 several races of the gall-forming organisms varying more or less 

 in amount of virulence and in adaptability to various hosts. In 

 general it is said that all plants susceptible to crown galls, i. e., 



