PYTHIUM 



103 



B 



ends of short branches of hyphae that sprout from the 

 host plant into the open air (see Fig. 33). There is 

 a beak at the apex of each sporangium; this beak 

 swells, and becomes a sac for the reception of the whole 

 protoplasmic contents of the sporangium (Fig. 33, B). 

 The contents of the sac split up 

 into a number of unwalled cells, 

 and each of these cells becomes 

 an active zoospore furnished 

 with a pair of cilia. These de- 

 velopments can occur only when 

 there is sufficient water to cover 

 the sporangia. The zoospores 

 swim about for a short time, 

 after which they cease to move ; 

 in germination they develop 

 hyphae which, when opportunity 

 favours, will carry on the vicious 

 parasitism of their kind. If 

 water is not sufficient, the 

 sporangia of P. Baryanum, 

 although prevented from pro- 

 ducing zoospores, are not de- 

 feated ; they Overcome the ^Branch of the mycelium with 

 j. 1,1 i -r , i three sporangia (s), x 125; 



difficulty by immediately grow- B , sporangium (^discharging 



ing into new hyph.83. Indeed, contents (6), which have be- 

 T . ., . come zoospores, x 145; C. 



the sporangium, in this event, an O6spore (osp} producing 



becomes an asexual Spore, an asexual sporangium (s), 



termed, in botanical parlance, 



a " conidium " (Gr. Jconis, dust). Thus Pythium in its 

 determination to live and multiply displays much 

 versatility and incidentally gives us an insight into the 



FIG. 33. PYTHIUM. 



