92 



BOTANY 



centrosome of the fertilised egg- cell appears to be derived from that of the 

 .s[>ermatozoid only. 



FIG. 97. A, An asexual swarm-spore 

 of Ulothrix zonata ; B, \, a gamete ; 

 2 and 3, conjugating gametes ; 4, 

 zygote, formed by the fusion of 

 two gametes, (x 500.) 



FIG. 98. A, Spermatozoid of Cham 

 fruijilis ; B, Spennatozoid of the 

 Fern, Onodeastruthiopteris. (After 

 SHAW.) The nucleus (k) is more 

 deeply shaded ; c, the cytoplasmic 

 portion ; c7, cilia which in B arise 

 from the tinner edge of the spiral 

 band ; 6, vesicle. (A x 540, 

 JB X 850.) 



Kio. 00. Fertilisation of a phanerogamic Angio- 

 sperm, somewhat diagrammatic. .-1, End of 

 pollen tube ; in it the generative cells gz, each 

 of which contains a sperm nucleus : //., til-- 

 vegetative nucleus in process of dissolution. 

 B-D, Egg in successive stages of fertilisation, 

 B, showing the generative cell with its 

 sperm nucleus, nk, penetrating the egg; syn, 

 the degenerating synergidae; C, the union of 

 sperm nucleus, sk, and egg nucleus, ek ; D, 

 the germ nucleus, kk, resulting from the 

 fusion of the sperm and egg nuclei; cJi, 

 rudiments of chromatophorcs. ( x about 500.) 



The nuclei of the sexual cells always possess only the reduced number of 

 chromosomes. By fertilisation the number becomes doubled, and after a shorter 

 or longer period is again halved in the reduction division. 



