62 BOTANY. 



ance in the protoplasm of delicate lines dividing it into numerous polyg- 

 onal areas which soon become more distinct, and are seen to be distinct 

 cells whose outlines remain more or less angular on account of the mutual 

 pressure. When ripe, the end of the sporangium opens, and the contained 

 cells are discharged (Fig. 36, C). In case they have no membrane, they swim 

 away at once, each being provided with two cilia, and resembling almost 

 exactly the zoospores of the white rust (Fig. 36, D, E). When the cells 

 are surrounded by a membrane they remain for some time at rest, but 

 finally the contents escape as a zoospore, like those already described. 

 By killing the zoospores with a little iodine the granular nature of the 

 protoplasm is made more evident, and the cilia may be seen. They soon 

 come to rest, and germinate in the same way as those of the white rusts 

 and mildews. 



As soon as the sporangium is emptied, a new one is formed, either by 

 the filament growing up through it (Fig. 36, F) and the end being again 

 cut off, or else by a branch budding out just below the base of the empty 

 sporangium, and growing up by the side of it. 



Besides zoospores there are also resting spores developed. Oogonia 

 like those of Vaucheria or the Peronosporece are formed usually after the 

 formation of zoospores has ceased ; but in many cases, perhaps all, these 

 develop without being fertilized. Antheridia are often wanting, and even 

 when they are present, it is very doubtful whether fertilization takes 

 place. 1 



The oogonia (Fig. 36, 6r, II) arise at the end of the main filaments, or 

 of short side branches, very much as do the sporangia, from which they 

 differ at this stage in being of globular form. The contents contract to 

 form one or several egg cells, naked at first, but later becoming thick- 

 walled resting spores (//). 



1 The antheridia, when present, arise as branches just below the oogo- 

 nium, and become closely applied to it, sometimes sending tubes through 

 its wall, but there has been no satisfactory demonstration of an actual 

 transfer of the contents of the antheridium to the egg cell. 



