FORMATION OF SPORES 61 



nucleus remains undivided and forms the nucleus of a 

 zoospore. The zoospores are formed, according to Biisgen, 

 by simultaneous division of the protoplasm contained in 

 the zoosporangium into several distinct portions. Accord- 

 ing to Rothert, the zoospores of Saprolegnia are diplanetic, 

 or have two distinct periods of movement. During the 

 first period they have two cilia of equal length inserted at 

 the summit. After a short period of activity the spore 

 becomes clothed with a thin membrane. The zoospore 

 then emerges through a narrow slit in this membrane, 

 furnished with two cilia of unequal length, and inserted 

 laterally. After a second short period of motility, the 

 zoospore comes to rest, forms a new membrane, and is 

 at once capable of germination. The zoospores of the 

 Peronosporeae, including Pythium^ are monoplanetic, or 

 have only one period of motility, which corresponds to the 

 second stage of those of the Saprolegniaceae. After the first 

 period of motility of the zoospores in the Saprolegniaceae 

 the cilia are withdrawn into the zoospore. In the second 

 condition in Saprolegnia^ and at the end of the only motile 

 phase in the Peronosporeae, the cilia are not absorbed by 

 the zoospore, but remain outside and disappear. 



In Myrioblepharis par ado xa Thaxter states that the 

 zoospores are thickly covered all over with cilia. This 

 structure is unique in the fungi, and elsewhere only occurs 

 in Vaucheria, an alga. 



Conidia generally may be distinguished from chlamy- 

 dospores by having a thin cell-wall, and by being terminal 

 on more or less specialised branches called conidiophores. 

 The majority of conidia are formed by acrogenous abjunc- 

 tion, or the delimitation of an apical portion of the hypha, 

 which becomes a conidium. Conidia may be produced 



