38 PROTISTS AND DISEASE 



showing that it is a sporangium ; the other imspecialised 

 swellings are called conidia ; in shape these are not at first 

 different from the oogonia, but the latter appear a little 

 later than conidia and are soon distinguished by the presence 

 of an aiitheridium, Fig. 6, d, near each of them, and the 

 subsequent formation of encapsuled oospores within them, 

 Fig. 7, /. Left alone the conidia remain dormant, and they 

 are able to resist frost, but not complete desiccation. 

 If fresh oxygenated water be added they germinate by 

 extrusion of the endospore into a hypha. If they are detached 

 as soon as ripe and placed in fresh water they produce each 

 a brood of zoospores. We have seen that a single zoospore 

 of Saprolegnia could be replaced by a hypha, and here it is 

 seen that a single Pythium-hypha may be replaced by a 

 group of zoospores. Some conidia of P. debaryanum have 

 the power of remaining dormant for long periods, and such 

 are at times distinguished by a slightly thicker wall, and 

 are termed " resting conidia." 



Sporangia germinate as a small brood of zoospores, if 

 they are supplied with plenty of well- oxygenated water in 

 a strong light. The stages are like those of Saprolegnia 

 with an additional feature, the distension of the apex of the 

 beak into a bubble or vesicle by cell-sap, and the passage of the 

 sporangial protoplasm into the vesicle there to break up 

 into zoospores, Fig. 6, e. Rotation occurs before the proto- 

 plasm passes into the vesicle during the stage of early 

 segmentation ; the homogeneous stage occurs about 5 



