128 MARGARET C. FERGUSON 



resulting in the formation of twelve nuclei under the direct in- 

 fluence of the egg-cytoplasm, rather than three divisions with 

 the formation of eight nuclei as has been previously described. 

 The phylogenetic bearing of this phenomenon may be more 

 far-reaching than is at first apparent, suggesting as it does a 

 possible closer relationship with those lower gymnosperms in 

 which many free nuclei arise in the egg before the deposition 

 of cell-walls. 



At present I can give only this general outline of the origin 

 of the proembryo, but I hope to be able in the near future to 

 make a detailed study of the several mitoses which occur here 

 in Pinus. 



The Fate Within the Egg of the Smaller Sperm-nucleus , 

 the Stalk-cell^ and the Tube-nucleus. When the various ele- 

 ments from the male gametophyte first enter the oosphere, there 

 is no question as to the identity of the several nuclei to one who 

 has become familiar with them before their exit from the pollen- 

 tube (figs. 213-215, plate XIX). Remnants of these cells have 

 been found in the upper part of the egg as late as the forma- 

 tion of the eight-celled stage of the proembryo. The stalk- 

 cell remains for some time unchanged and finally disintegrates. 



In so far as I have been able to determine, it assumes a more 

 or less granular appearance, and at last blends with the cyto- 

 plasm of the egg. The tube-nucleus undergoes various changes. 

 Occasionally it seems to contract, becoming gradually smaller 

 until it is no longer demonstrable ; it may change little, if any, 

 in size, but its reticulum often becomes more prominent than 

 when within the pollen tube ; rarely it enlarges rapidly after its 

 entrance into the egg and develops a beautiful reticulum (fig. 

 212, plate XIX). The sperm-nucleus not active in fertilization 

 increases but little in size, and its network becomes less dense, 

 resembling that of the conjugating nuclei ; it may pass through 

 the ordinary processes of disintegration ; and in a few cases it 

 has been observed to divide amitotically, as described by Ar- 

 noldi ('GO) in Cephalotaxus. 



But frequently the sperm-nucleus and occasionally the tube- 

 nucleus attempt to divide mitotically. One or two small, abor- 

 tive, karyokinetic figures are not uncommon in the upper part 



