GYMNOSPERMS. 



'57 



being due to a greater need of food material by this part of the central 

 cell ; for it is here that the greatest activity takes place during the 

 maturing of the egg-cell, which culminates in the formation of the 

 ventral canal-cell. Webber does not find any protoplasmic connections 

 between the egg-cell and those surrounding it in Zamia, and so far 

 as the author is aware no such protoplasmic connections exist in the < 

 higher Gymnosperms. In Cycas the phenomenon described by Ikeno 

 is, if true, probably an adaptation to the rapid transfer of nutritive 

 material from the surrounding cells to the egg-cell. 



Strasburger ('01, pp. 550-553), in a late publication on the proto- 

 plasmic connections between cells in plants, calls into question the 

 statement that nuclei or nuclear fragments pass bodily through the pits 

 of the surrounding cells into the egg-cell of Gymnosperms as a normal 

 phenomenon, and asserts that it is the result of injury due to pressure 

 or fixing reagents. 



There seems to be no doubt that in all Gymnosperms in which the 

 egg-cells reach such an enormous size the cells immediately surround- 

 ing the egg contribute directly to the nutrition of the latter, but it is 

 not clear why any of the material should pass over bodily into the 

 egg-cell. 



The final step in the development of the archegonium is the forma- 

 tion of the ventral canal-cell, which takes place immediately preceding 

 fecundation, and consequently this cell persists only a short time (Fig. 

 67, A). It was probably due to this fact that the presence of a ventral 

 canal-cell was not observed by Warming and Treub. Only a plasma 

 membrane and not a cell-wall is formed separating the ventral canal- 

 cell from the egg. It is not at all improbable that in some cases a 

 plasma membrane may not be formed, and such is reported for Ceph- 

 alotaxis fortuni by Arnoldi (1900). The formation of a plasma 

 membrane is, however, of secondary importance in the formation of 

 the ventral canal-cell, for if the nucleus of the central cell of the 

 archegonium divides karyokinetically, and one of the daughter-nuclei 

 becomes the functional egg-nucleus, the division is certainly to be 

 regarded as the formation of a ventral canal-cell whether a plasma 

 membrane is formed or not. 



Botanists have sometimes been inclined to refer to the formation of 

 the ventral canal-cell as a maturation process similar to that in the 

 animal egg. Ikeno speaks of this step in the development as the period 

 of maturation (Reifungsperiode), which recalls the formation of the 

 polar bodies in the animal egg, but I do not infer that he considers the 

 two processes homologous. He states, however, that it appears prob- 



