'58 



ARCHEGONIATES. 



able, judging from the karyokinetic figures observed, that the nuclear 

 division leading to the formation of the ventral canal-cell is of the 

 heterotypic type, and takes place essentially as in the first division of 

 the pollen mother-cells of the Liliacece. This is certainly an error, 

 for in both Gymnosperms and Angiosperms the heterotypic nuclear 

 division occurs in the micro- and macrospore mother-cells and nowhere 

 else in ontogeny. Since the spore mother-cells of the Gymnosperms 

 are homologous with those of the higher plants, we naturally expect 

 to find the heterotypic division in Cycas in the first karyokinesis of 

 the macrospore mother-cell. This is made all the more certain by the 

 researches of Juel (1900), who finds in Larix that the first nuclear 

 division in the macrospore mother-cell is heterotypic. In Larix and 



A B 



FIG. 65. Upper end of nucellus ; spermatozoids in pollen tube of Zamia. (After Webber). 



A, diagrammatic outline of upper end of nucellus, showing proximal ends of pollen tubes growing down 



into the cavity just above archegonia ; a, archegonia ; p, prothallium ; pc, pollen chamber ; ft, pol- 

 len tubes ; pg, pollen grain. 



B, two mature spermatozoids in proximal end of pollen tube. 



in other Gymnosperms the earlier development of the macrospore is 

 precisely the same as in such Angiosperms as Helleborus, in which 

 the first nuclear division is heterotypic and homologous with the first 

 division in the pollen mother-cell. 



The formation of the ventral canal-cell may represent some sort of 

 a maturation process, and the conclusion that this cell is an aborted 

 egg is tempting, but at our present state of knowledge such an infer- 

 ence is scarcely justifiable. 



FECUNDATION. 



Soon after its formation the ventral canal-cell disorganizes. The 

 nucleus of the egg passes back gradually toward the middle of the cell, 

 at the same time increasing in size. Finally, when the center of the 

 cell is reached, the nucleus is usually large, being generally longer 

 than broad, and shows the structure of the resting condition. 



