330 GYMNOSPERMS 



the mitosis could hardly have escaped observation, had it been 

 present. 



There can be no doubt that in the evolution of the archegonium 

 there has been a gradual reduction in the length of the neck and in 

 the number of neck canal cells, which, phylogenetically, are prob- 

 ably eggs. In the lower Filicales there are two neck canal cells; in 

 the higher homosporous forms, only one neck canal cell with two 

 nuclei; and in the heterosporous genera, even the mitosis has failed 

 to take place, so that there is only one neck canal cell with one 

 nucleus. In the gymnosperms the mitosis which, in the pterido- 

 phytes, gives rise to the neck canal and ventral series, is suppressed, 

 so that the ventral canal mitosis takes place in the cell which, in 

 Pteris, gives rise to a primary neck canal cell and a central cell. 



There can hardly be any doubt that the ventral canal cell is a re- 

 duced egg, just as in Taxus, and several other genera with unequal 

 sperms, the smaller sperm is strictly the homologue of the larger one. 

 In tracing the evolution of the archegonium, the bryophytes show a 

 nearly equal division, so that the egg and ventral canal cell can be 

 distinguished only by their relative positions; and, in a few cases, 

 there are several equal eggs. 



After the ventral canal mitosis, fertilization follows promptly, the 

 interval between the mitosis and fertilization usually not exceed- 

 ing 5 days. 



