MORPHOLOGY 



67 



the nucleus of the fertilised egg-cell. The cytoplasm of the male 

 cell also commingles with that of the female cell,' but the chroma- 

 tophores of the embryo are derived from the egg-cell alone. It is 



// 



^h 





A 



Fig. 69.— A, An asexual swarm-spore 

 of Ulofhrixzonata; B, 1, a gamete ; 

 2 and 3, conjugating gametes ; 4, 

 zygote, formed by the fusion of 



two gametes, (x 500.) 



I V 



Fig. 70.-^4, Spermatozoid of Chara 

 fragilis; B, spermatozoid of the 

 Fern Phegopteris Giesbrechtii. The 

 darker portion, Jc, corresponds to 

 the cell nucleus ; the lighter, 

 c, to the cell cytoplasm ; d, cilia ; 

 b, vesicle, (x 540.) 



Fig. 71. — Fertilisation of a phanerogamic 

 Angiosperm, somewhat diagrammatic. 

 A, End of pollen tube; in it the genera- 

 tive cells gz, each of which contains a 

 sperm nucleus; vie, the vegetative cell 

 in process of dissolution. Jl-D, Egg in' 

 successive stages of fertilisation, — B, show- 

 ing the generative cell with its sperm 

 nucleus, sk, penetrating the egg ; C, the 

 union of sperm nucleus, sic, and egg 

 nucleus, el; ; c, centrospheres ; D, the 

 germ nucleus, Tele, resulting from the 

 fusion of the sperm and egg nuclei ; eft, 

 rudiments of chromatophores. (x circa 

 500.) 



still uncertain whether a similar fusion of the centrospheres of the 

 sexual cells also takes place. It is regarded as more probable that 

 the centrospheres of the egg nucleus — more rarely those of the sperm 

 nucleus — become functionless, so that the centrospheres of the fertilised 

 egg are derived only from the sperm nucleus, or from the nucleus of 

 the female cell. 



