236 A TEXTBOOK OF THEORETICAL BOTANY 



The fungal mycelium is intercellular, like that oi Peronospora, and sends 

 haustoria into the cells of the host plant ; these haustoria are fairly well 

 developed and end in button-like projections in the host cells. It is through 



Fig. 227. — Cystopus candidiis on Copsella 

 showing white pustules and distortion of 

 the stem. 



them alone that the Fungus obtains its nourishment. It spreads rapidly 

 within the host and may attack all parts of the plant, besides those where the 

 white patches are apparent. Reproduction is both sexual and asexual, though 

 there is no alternation of generations. 



Asexual Reproduction 



The asexual reproductive organs are developed just below the epidermis 

 of the stem or leaf of the host plant. In this position short sporangiophores 

 are produced in compact groups, forming an almost complete tissue. As 

 growth continues a nucleus passes to the tip of each sporangiophore, and this 

 is followed by a deepening constriction around the tip, thus cutting off a 

 zoosporangium with one nucleus. Immediately behind, another zoo- 

 sporangium is cut off in the same way, until chains of sporangia have been 

 formed, one above the other, from each sporangiophore (Fig. 228). The 

 outer layer of the wall of the sporangium becomes gelatinous, and as a result 

 the sporangia tend to stick to one another. 



The growing pressure of all these zoosporangia cut off below the epidermis 

 finally causes it to lift up, then to split and break up, exposing the white 



