130 MARGARET C. FERGUSON 



animal side, that the stimulus to division is given not by the egg- 

 nucleus, but by the cytoplasm of the egg. If this be true, it is 

 not strange that these nuclei, lying in a position where everything 

 is rhost favorable for growth and development — in a medium 

 not only rich in nutritive substances but especially adapted to 

 incite activit}'' in nuclei — should divide. It is a well-known 

 fact that when several spermatozoa enter the ovum of certain 

 animals, only one unites with the egg-nucleus, the others de- 

 generate, or, as is frequently the case, they divide mitotically. 

 And herein we find a further similarity between the processes 

 attending fertilization in some animals, and those taking place 

 within the oosphere of Pinus. 



SUMMARY. 



At the time of fertilization, an opening is formed in the apex 

 of the pollen-tube, and the cells of the male gametophyte which 

 still persist, together with a portion of the cytoplasm and some 

 of the starch of the pollen-tube, pass into the cytoplasm of the 



The larger sperm-nucleus escapes from the protoplasm of the 

 sperm-cell and moves directly toward the egg-nucleus ; the 

 other nuclei from the pollen-tube may persist, in a modified 

 form, in the upper part of the archegonium until the eight- 

 celled stage of the proembryo ; but the cytoplasm of the sperm- 

 cell soon fuses with that of the oosphere. The stalk-cell grad- 

 ually disintegrates and blends with the egg-cytoplasm. The 

 tube-nucleus and the smaller sperm-nucleus may share the fate 

 of the stalk-cell, but, during the second division of the egg, they 

 not frequently give rise to mitotic figures. The smaller sperm- 

 nucleus, then, may pass through a slow process of disintegration, 

 it may divide amitotically, or it may give rise to a karyokinetic 

 figure of more or less definiteness. 



There is no apparent change in the diameter of the sperm- 

 nucleus after its entrance into the oosphere. At the time of 

 conjugation, the egg-nucleus is several times larger than the 

 sperm-nucleus, and the sperm-nucleus does not increase in size 

 after its contact with the egg-nucleus. The inequality in size 

 of the sexual nuclei may be due to the difference in the size of 



