LIFE HISTORY OF PINUS II5 



but as a rule, the conjugation-nuclei in the pines, as observed 

 by Arnold! ('oo) in Cephalotaxus, differ in size only (figs. 

 215-223, a). 



Just before the sexual nuclei come into contact, the side of 

 the egg-nucleus adjacent to the sperm-nucleus becomes slightly 

 concave (fig. 216). This concavity is doubtless formed under 

 the influence of the approaching sperm-nucleus and suggests 

 the crater-like depression developed at an earlier period in the 

 egg-nucleus of Cycas (Ikeno, '98). As noted by Blackman, 

 the sperm-nucleus does not penetrate the membrane of the egg- 

 nucleus, but it lies in a pocket-like indentation formed as a 

 result of the contact of the two nuclei in the side of the oosphere- 

 nucleus. Thus both nuclei though still perfectly distinct and 

 lying side by side, come to occupy the space originally filled 

 by the egg-nucleus. The sperm-nucleus, when in contact with 

 the nucleus of the egg, ordinarily assumes the form of a bicon- 

 vex lens, but it may vary much in outline, presenting in some 

 cases the figure of a crescent, and in others, that of an ellipse. 

 Occasionally it forms a deep, tongue-like depression in the 

 nucleus of the oosphere (figs. 214-223, a). 



THE FIRST DIVISION FOLLOWING FECUNDATION. 



The Prophases of the Division, — When the sexual nuclei come 

 to lie in intimate contact, but are still, to all appearances, per- 

 fectly distinct, certain changes in their structure indicate that 

 each is in the early prophase of division. The chromatin con- 

 denses or collects in irregular granules about the periphery of 

 the sperm-nucleus, while that of the egg-nucleus is deposited 

 just beneath the sperm-nucleus. The remainder of each nucleus 

 is filled with a granular, achromatic reticulum of great beauty, 

 reminding one of delicate frost work (fig. 224). This condition 

 suggests an early stage of fertilization in the sea-urchin as de- 

 scribed by Wilson ('95). Wilson thinks that the sudden increase 

 in linin may be only apparent, resulting from the " rapid con- 

 densation and localization of the chromatic substance " ; but he 

 is inclined to believe that "a considerable portion of the chro- 

 matin breaks down at this time into linin." It would appear 

 that the prominence of the achromatic reticulum in the conju- 



