694 



FUNGI 



it consists of generally non-septate, branched hypha, which 

 derive their nourishment from the cell-contents of the plant 

 through which they ramify. For a short time the fungus is 

 confined within the body of the diseased seedling, but after 



extending itself through all parts of 

 the latter, the hyphse grow out into 

 the surrounding moist air and are 

 able to reach across short distances 

 to healthy neighbouring plants, which 

 they immediately penetrate ; in this 

 manner the disease can spread from 

 plant to plant. Moreover, the top- 

 pling over of the afifected seedlings 

 ,J brings the fungus into contact with 

 adjacent plants, and aids the distribu- 

 tion of the disease. 



After a few hours the tips of the 

 hyphje give rise to the following re- 

 productive organs : — 

 (i) conidia. 



(2) sporangia. 



(3) oospores. 

 Each conidium is a round or 



slightly oval spore {f. Fig. 233), 



F,G. ^33.-.!, a portion of the my- which, ou germination, gives rise to 



«"hyph/;^r-"n1dia1 f SS ^ hyphal filament, or germ-tube, 



^^■■SpoS"^ri;LideSk"^ii" capable of penetrating seedlings and 



minated portion/; e zoospores; og giving rise to a new mycelium. 



oogonium ; / periplasm '^os oospnere ; o o J 



a antheridum ; t ferlilising-tube 



ripe oospore in the oogonium og. (All 

 enlarged about 130 diameters.) 



A sporangium is similar to a 

 conidium in form and size, but 

 when placed in water its wall bulges out and forms a 

 bladder-like process into which the contents of the sporan- 

 gium are transferred; the protoplasm then divides into a 

 number of r^ospores, or sivarmspores, which are subsequently 



