THE FUNGI WHICH CAUSE PLANT DISEASE 95 



them the pumpkin, squash, cucumber, muskmelon, watermelon, 

 gourd, in fact according to the work of Selby '"^ any cucurbit ap- 

 pears hable to attack. Clinton infected muskmelons with spores 

 produced on cucumber. The fungus is especially prevalent on 

 cucumbers raised under glass. 



Bremia Regel (p. 84) 



As in Peronospora except that just below the ends of the conidio- 

 phore branches there are pronounced swellings from which spring 

 radially a number of short branches each 

 bearing an ovate, papillate conidium. The 

 conidia germinate by apical germ tubes. 

 There is only one species. 



B. lactucae Regel is found on lettuce and 

 several othei- Compositae."'^ It is more in- 

 jurious in Europe than in America. 



Hypophyllous or amphigenous, causing 

 discoloration, then wilting of the host; conid- fig. 65.— B. lactucs. 

 iophores produced singly but in great abun- ■^t®'' Tubeuf. 

 dance, much branched; conidia ovate, 16-22 x 15-20 ju; oospores 

 small, 26-35 n, light brown, the epispore wrinkled. 



Peronospora Corda (p. 84) 



52 



This genus of some sixty species contains several aggressive 

 parasites. Its conidiophores are much like those of Plasmospara 

 but with more tendency to dichotomous branching and to more 

 graceful habit; the apices are acute. 



Mycelium well developed, haustoria filiform, simple or 

 branched; conidiophores dichotomously 2-10 times branched at 

 acute angles, ultimate branchlets acute, more or less reflexed; 

 conidia hyaline or colored, papillate, germinating directly by lateral 

 germ tubes; oospores globose, reticulate, tuberculate, wrinkled or 

 smooth. 



P. parasitica (Pers.) De Bary.^^ This is often associated with 

 Albugo Candida, giving it the appearance of a parasite on that 

 fungus. Almost all species of Cruciferse are subject to attack, 

 among them cabbage, cauliflower, radish, collards, turnips, horse- 



