1917I STEVENS— PLANT PATHOLOGY 305 



mushroom 



and live in the sap; as cabbage, cucurbit, and 



and 



part of this paper which may lay any claim to originality, would 



present the following suggestions as a step toward a classification 



of plant diseases caused by fungi, separating them into the following 

 categories: 



Wilt diseases due to m 



bundles by parasites. These may be called cases of embolism; for 



and Acrostilagmus 



campestris 







2. Disintegration of the xylem structures; for example, the 

 ious wood rots due to Thelephora, Hydnum, Porta, Poly poms. 



phyllitm 



tained within 



asm of the host cell. This is the strictest type of parasitism, 



example, diseases due to Synchytrium. 



parasitism; for 



from 



living cells by haustoria, which may be called endocellular haustorial 

 parasitism; for example, diseases due to Phyllactinia, Peronospora, 

 Albugo y and Plasmopara. In this group the conspicuous feature 

 is the relatively large development of the haustorial surface as 



m 



5. Diseases in which the live epidermal cells only are directly 

 parasitized. These may be called cases of epidermitis, for example, 

 diseases due to the Erysiphales (exclusive of Phyllactinia), Meliola. 



6. Diseases in which the parasite grows between the living 

 host cells. Haustoria may be present, but if so they are not 

 prominent, and the apparently dominant part of the absorptive 

 system is the intercellular mycelium. This may be called inter- 



exam 



Ceph 



7. Diseases in which the host tissue is displaced or replaced by 

 fungous masses. This may be called mvcosclerosis; for example, 



'•P 



which may be called tumor. 



tumefi 



y 



