FERTILIZATION 





Riccia, Meyer (1911) on Corsinia, Graham (1918) on Pn and 



Woodburn (1920) on Reboulia. It appears thai in bryophytea the body 



of the biciliate spermatozoid, which consists mainly of nuclear material, 

 undergoes in the egg cytoplasm a 1 ransformal ion into ,-i pel iculate nucleus 

 before fusing with the egg nucleus (Fig. 117). The fat-' of the non- 

 nuclear structures (cytoplasm, blepharoplast, and filial i< not known 

 with certainty, but it is probable that they arc absorbed in Up 

 plasm. In the liverwort, Preissia 

 quadrata, Miss Graham has found 

 two centrosomes with weakly de- 

 veloped asters in the cytoplasm of 

 the egg at the time the two pronuclei 

 are about to fuse (Fig. 23, A). It is 

 not known what relation their ap- 

 pearance may have to the entrance 

 of the spermatozoid. 



The most detailed account of fer- 

 tilization in a pteridophyte is that 

 given by Yamanouchi (1908) for 



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Fig. 117. Fio. 118. 



Fig. 117. — Fertilization in Anthoceros. Male and female pronuclei about c> fuse in 

 lower part of egg in venter of archegonium; elongated plastid above them. Gametopl 



cells show one nucleus and one plastic! each. X 10.50. 



Fig. 118. — Fertilization in Nephrod&utn. 

 A, spermatozoid entering egg nucleus. B, spermatosoid becoming retioulate in n 



of female reticulum. {After Yamanouchi, 1908.) 



Nephr odium (Fig. 118). In Nephr odium the multiciliate Bpermatosoid 

 enters bodily into the egg nucleus with do previous alteration into the 

 reticulate state. Here it gradually becomes reticulate and irregular in 

 shape, until finally its limits are indistinguishable, the chromatic material 

 contributed by the two gametes apparently forming a Bingle fine-meshed 

 network. 



Gymnosperms. — Among living gymnosperms the Cycadales and 

 Ginkgoales are characterized by the possession of motile spermatoaoids. 



