LIFE HISTORY OF PINUS 125 



retain their position in the upper half of the egg until their 

 growth is completed (fig. 249). Here, again, as in the develop- 

 ment of the two segmentation nuclei, the steps described for the 

 maturation of the egg-nucleus are repeated, except that a 

 nucleolus does not generally become apparent within these 

 nuclei. After attaining full size, the four nuclei pass to the base 

 of the oosphere, as described by all recent writers. During their 

 descent many fibers arise in the cytoplasm surrounding the 

 nuclei. Some of these threads run parallel with the walls of 

 the nuclei, while others extend out from the nuclei in a radial 

 manner. These fibers become more prominent as the nuclei 

 approach the base of the oosphere, and, as in the case of the 

 egg-nucleus, they are most strongly developed along the upper 

 sides of the nuclei (figs. 250, #-251, b}. Blackman suggests a 

 relation between these fibers and the walls that arise later at 

 the organic apex of the oosphere, but I find no evidence of 

 any connection between the two. When these nuclei have 

 nearly reached the bottom of the egg, the nutritive spheres 

 have almost disappeared from the cytoplasm, those which 

 still persist being much reduced in contents (fig. 251, a). 

 After the four nuclei have arranged themselves at the " organic 

 apex " of the oosphere, in a plane perpendicular to the major 

 axis of the archegonium, a marked change occurs in the cyto- 

 plasm of their immediate vicinity. It becomes dense, coarse, 

 more or less granular, and has a great affinity for stains (figs. 

 252, a and 3, plate XXIII). 



The early prophases, as also the meta- and anaphases in the 

 mitosis of the four segmentation nuclei, in so far as studied, 

 correspond in every respect with the same stages in the second 

 division following fertilization ; and it is probable that the 

 chromosomes are derived from two distinct spiremes as in the 

 first and second divisions occurring within the egg ; but, as 

 already indicated, the steps in the origin and development of 

 the chromosomes have not been carefully traced in this division. 

 These nuclei divide simultaneously. Chamberlain states that 

 "in the division of the four nuclei the spindle is extremely 

 broad and multipolar." I have occasionally observed such a 

 figure during this mitosis, but here, again, great variation exists. 



