22 



MORPHOLOGY OF SPERMATOPHYTES 



20, (7, D). These cells have dense cytoplasm and larger nuclei, 

 but the very thick cellulose wall toward the central cell is 

 pierced by pores through which cytoplasmic threads connect 

 with the cytoplasm of the central cell. This continuity of cyto- 

 plasm between the jacket cells and the central cell in Cycads 

 was demonstrated by Goroschankin, 12 and is confirmed by 

 Ikeno. In connection with his work on the embryogeny of 

 Cycas circinalis, Treub 11 - 14 noted the heavy and pitted wall 

 bounding the central cell, and really demonstrated the conti- 

 nuity of the cytoplasm through it. Before the archegonium has 

 reached its full development the nuclei of the jacket cells show a 

 delicate chromatin network, but after a time they become ho- 

 mogeneous, showing no differentiated structure except the nucle- 

 olus. The contents of the jacket cells, nuclei and all, now pass 

 through the pores into the central cell, which thus receives an 

 abundant supply of nutritive material (Fig. 20, C, D). The 

 nucleus of the central cell, at first very small, grows during the 

 three months until it reaches the great size of 75 to 120/x, in 

 diameter. At first it has a finely granular chromatin network, 

 but suddenly condenses, just as the nuclei of the wall cells, and 

 shows no nuclear structure excepting the nucleolus. Ikeno 

 calls attention to the fact that this process of nutrition recalls 

 that of many animals, in which it has been proved that dis- 

 solved nutrient material passes from the follicle cells to the egg. 



The third period in the preparation of the archegonium con- 

 sists of the formation of the ventral canal cell, which takes place 

 at the end of September, immediately before fertilization, and 

 lasts for a very short time. The central cell thrusts a beaklike 

 process between the neck cells, a spindle is organized at once, 

 and the small ventral canal cell is cut off rapidly, but for a long 

 time is distinguishable as a cap resting upon the ventral cell. 

 After the cutting off of the ventral canal cell the nucleus of the 

 large ventral cell passes to the central region of the organiz- 

 ing egg. 



It is of interest to note that the occurrence of a ventral canal 

 cell in Cycads remained in doubt until its demonstration by 

 Ikeno 20 in 1896 in Cycas revoluta, confirmed in 1897 by Web- 

 ber 27 for Zamia integrifolia. Strasburger 7 in 1876 observed 

 such a cell in Cycas sphaerica; Warming 8 described it in 1877 

 in Ceratozamia robusta, but two years later 9 withdrew his con- 



