ii8 PLANT LIFE. 



the meantime escaped into the water, swarm round the 

 oospheres in considerable numbers, and by their move- 

 ments impart to them a rotatory movement which lasts for 

 some time. Eventually one or more of the antherozoids 

 become blended with the substance of the oosphere and 

 fertilize it; after which a cell-wall of cellulose is formed, and 

 without a period of rest commences to germinate. It is 

 stated that unfertilized oospheres show indications of 

 germination, which however never proceed far before they 

 perish. 



In many species cavities exactly resembling in structure 

 the conceptacles are present, but produce no sexual organs. 

 These are sometimes termed cryptostomata, and may be 

 considered as abortive conceptacles. 



Coufervoidese Heterogamse. 



All the species included in the present order inhabit 

 fresh water, are small in size, and have bright green un- 

 masked chlorophyll. They form a connecting link between 

 the Isogamous Confervoidere and the simpler Florideas, 

 differing from the former in having well-differentiated male 

 and female organs of reproduction, and from the latter in 

 having the male sexual organs motile and furnished with 

 cilia, and in having asexual motile ciliated zoospores. 

 The thallus consists of a filament of superposed cells, 

 either simplfi or branched, or of a flattened plate of cells 

 radiating from a centre, consequently exhibiting far less 

 differentiafion than in the two preceding orders, and the 

 reason f^^r their occupying the present position in the 

 scheme ofi classification rests on the sexual mode of repro- 

 duction iJ»esent in the highest members of the order, which 



