I 



CYCADALES 123 



The failure of wall formation at the ventral canal mitosis indicates 

 a more advanced stage in the reduction of the archegonium than 

 that found in Ginkgo, Pinus, and other forms which develop a defi- 

 nite wall between the two nuclei. 



It is interesting, in this connection, to recall the reduction of the 

 archegonium from forms with long necks, numerous neck canal cells, 

 and a definite ventral canal cell, as in Marchantia; through forms 

 like Riccia, with four neck canal cells, a ventral canal cell and an egg 

 cell ; through forms with only one neck canal cell and a ventral canal 

 cell and an egg cell, like Marsilia, where the next step brings the 

 condition in Ginkgo, with no neck canal cell, but with a ventral canal 

 cell and an egg cell. In this series one finds occasional binucleate 

 neck canal cells and, in related forms, a smaller number of neck 

 canal cells, so that there is first the failure of a wall to be formed be- 

 tween two nuclei, and then the failure of the division itself. In this 

 reduction, the cycads have gone a step farther than Ginkgo, which 

 still retains the wall between the ventral canal nucleus and that of 

 the egg. It is only when viewed in this way that it becomes a matter 

 of any evolutionary importance whether there is a ventral canal cell 

 and an egg cell, or merely two nuclei not separated by a wall. 



Comparative morphology leaves no doubt that the neck canal 

 cells and the ventral canal cell are homologous with the egg, so that 

 the archegonium, phylogenetically, contained several eggs. 



The neck itself keeps pace with the reduction of the neck canal 

 cells until, in the cycads, there are almost always just two neck cells; 

 but in Encephalarios villosus Sedgwick^-J^ found that the neck cells 

 rather frequently divide. One of his figures shows six neck cells. 



The neck cells grow rapidly and, in later stages, become very 

 turgid. 



To return to Dioon edule, which seems to be a typical cycad: the 

 nutrition of the egg is practically the nutrition of the central cell, for 

 the division of the nucleus of the central cell to form the ventral canal 

 nucleus and the egg nucleus takes place only a few days before fer- 

 tilization. So the process may be called the nutrition of the egg. 



For the first two or three months after the appearance of the 

 archegonium initials, food materials are received from the surround- 

 ing cell by the usual method of transferring substances from one cell 



