72 PRACTICAL BOTANY. 



brought from outside in the morning into the higher 

 temperature of the laboratory or working-room. There 

 are two modes of reproduction of this Alga by means 

 of zoospores, and they are readily distinguished by 

 the size of the motile cells. Thus there are to be 

 recognised 



1. The macro-zoospores, or asexual reproductive 

 cells : these are relatively large, spherical or pear- 

 shaped, green, primordial cells, furnished with four cilia 

 attached to the hyaline anterior end, in which there is 

 also a contractile vacuole. According to the bulk of 

 the filament, one, two, four, or perhaps sometimes eight 

 of these may be produced from a single cell : observe 

 how they escape by a lateral hole in the cell-wall, being 

 surrounded for a time by a membrane from which they 

 soon free themselves, and begin active movement : 

 finally they settle, form a cell- wall, and germinate 

 directly to form new individuals. 



2. The micro-zoospores or sexual gametes : these 

 are relatively small ; and according to the bulk of the 

 filament, eight, sixteen, or thirty-two of them may be 

 produced from each cell : observe how they also, after 

 passing through a lateral hole in the cell-wall, are at 

 first enveloped in a thin membrane, which is soon 

 burst, and they escape as- small pear-shaped motile 

 bodies with two cilia. Observe carefully how these 

 conjugate in pairs, coalescing first by their hyaline 

 ends, then along their whole length ; the resulting 

 zygospore still continues to move by its four cilia for 

 a time after conjugation, but finally settles down, and 

 forms a cell-wall in about two days. 



It will be difficult to observe the further growth 



