COMPARATIVE MORPHOLOGY OF GYMNOSPERMS 165 



plasm except the niicleus of the male cell, which advances toward 

 that of the egg and becomes imbedded in it. There is some 

 evidence that the fusion of the two nuclei does not involve a 

 fusion of their chromatin, and that the male and female chroma- 

 tin continues to exist as separate groups at the first segmenta- 

 tion of the fusion nucleus. How far this may be true of Gym- 

 nosperms in general it is impossible to say, but in any event it 

 is an interesting problem, involving not only a departure from 

 the habit of other known plants, but also a resemblance to the 

 phenomena of fertilization observed in certain animals, as 

 Ascaris. 



It is perhaps well to call attention to the fact that the cyto- 

 plasm of the male cell enters the cytoplasm of the egg and fuses 

 with it. The importance of this in connection with fertiliza- 

 tion is a matter of opinion rather than of demonstration. It is 

 certainly true that the nucleus of the male cell of Gymnosperms, 

 and probably of all plants, becomes relatively very large, being 

 covered by a thin layer of cytoplasm. Whether this cytoplasm is 

 directly necessary to fertilization, or merely necessary to the male 

 nucleus preceding fertilization, is a question for the future to 

 answer. 



IV. THE EMBRYO 



The germination of the oospore is one of the most character- 

 istic features of Gymnosperms, and although the details seem to 

 vary widely there is underneath them all a general method which 

 belongs to the group and has been observed in no other. A 

 natural series may be arranged, beginning with the Cycadaleg. 

 In them, germination begins with free nuclear division, fol- 

 lowed by the placing of the free nuclei in a cytoplasmic layer 

 which lines the wall of the oospore and surrounds a central cav- 

 ity. The free nuclei then organize a parietal layer of cells, 

 which are apt to be more or less massed at the base of the oospore 

 (towards the main mass of the endosperm), the whole of the endo- 

 sporic tissue being known as the proembryo. These basal cells 

 of the proembryo then begin a remarkable elongation, forming 

 the very long and massive suspensor, which bears at its tip the 

 group of cells which is to develop into the embryo proper. The 

 three regions of the embryo which thus appear are (1) the pro- 

 embryo, an endosporic structure, which relates the embryo to 



