THE ALG.E 



155 



female plant either near or actually upon the ob'gonium 

 (Figs. 66 and 69, A). The androspore surrounds itself 

 with a cell- wall and germinates. The plant which it 

 produces is always of very small size ; it may consist of 

 a basal vegetative cell with one or more antheridial cells, 

 or the vegetative part may be absent, and the whole 

 dwarf male be reduced to an antheridium only. In the 

 antheridial cell, or in each 

 of them if more than one 

 be present, two sperm- 

 atozoids are produced. 

 They escape by a lid-like 

 opening of the anther- 

 idium, and make their way 

 to the oogonial aperture 

 (Figs. 66 and 69, A). 

 Like the ordinary sperm- 

 atozoids, they ^ move by F io. 69.-A, fertilisation of 



a Crown of cilia ; they ium ciliatum ; cf, dwarf male 



are also able to help P lant fl ' which a spermatozoid 



r has escaped ; sp, the spermatozoid 



themselves along by the 



in con tact with the ovum, $. Mag- 

 nified 350. B, a single spermatozoki 

 showing cilia. Magnified 350. C, 

 germination of the oospore in Bid- 

 bochcete, showing the contents divided 

 up to form four zoospores. Magnified 

 250. (After Pringsheim.) 



contractions of their 



whole body. The same 



power of contraction is of 



service when the oogonial 



opening is reached, for 



the entrance may be much narrower than the body of 



the spermatozoid, which can only pass through by 



accommodating its form to the size of the passage. 



The act of fertilisation now takes place ; the 

 spermatozoid comes into contact with the protoplasm 

 of the ovum, and the two cells unite. The details of 

 fertilisation have been exactly followed in (Edogonium\ 



