THE FUNGI WHICH CAUSE PLANT DISEASE 



25 



not a gas or acid producer, gelatine liquefied. Cavities are formed 

 around the bundles but the organism seems to be only feebly 

 destructive to cellulose. A brown pigment is produced in the 

 host plants and on steamed cruciferous substrata. Growth 

 rapid on steamed potato cylinders at room temperatures, without 

 odor or brown pigment. Growth feeble at 7°, rapid at 17 to 19°, 

 luxuriant at 21 to 26°, very feeble at 37 to 38° and ceases at 40°. 

 T. D. P., 10 min., 51°. 



Fig. 12. — Ps. campestris. .Section of a cabbage leaf par- 

 allel to the surface and near the margin, showing the 

 result of infection through the water-pores. After 

 Smith. 



It is closely related to Ps. hyacinthi from which it differs chiefly 

 in its pathogenic properties, its duller yellow color and its higher 

 thermal death point. It is troublesome upon cabbage, turnips, 

 cauliflowers, collards; and a very large number of cruciferous 

 hosts, both cultivated and wild are susceptible. It enters the host 

 plant through the vascular system which becomes decidedly 

 brown. 



This organism was first isolated by Pammel ^^ (see also ") from 

 rutabagas and yellow turnips in 1892; green-house inoculations 

 with pure cultures were made in scalpel wounds, which were then 



