114 MARGARET C. FERGUSON 



of the " sperm-cells, "passed into the egg along with the sperm- 

 nuclei but he was unable to demonstrate the fact. There can be 

 no doubt that the cytoplasm of the sperm-cell enters the egg in 

 Ftnus (fig. 212). This cytoplasm very soon fuses with that of 

 the egg and the larger sperm-nucleus moves towards the nucleus 

 of the oosphere ; the other elements from the pollen-tube remain 

 for some time in the upper part of the ovum. There is no evi- 

 dence that the sperm-nucleus increases in size after entering the 

 oosphere ; neither is their an increase in stainable substance, but, 

 on the contrary, the nucleus loses its dense structure ; and occa- 

 sionally a nucleolus becomes apparent within it. (Compare the 

 sperm-nuclei in figs. 212 and 213 with those in figs. 215-223, .) 

 Union of the Sexual Nuclei. There is every indication that 

 the movement, within the egg, of the sperm-nucleus which be- 

 comes active in fertilization is both rapid and direct. It almost 

 invariably traverses the shortest distance between its point of 

 entrance into the egg and the egg-nucleus. The relative posi- 

 tion which the conjugating nuclei may occupy with reference 

 to the major axis of the oosphere varies considerably, but 

 always bears a definite relation to the position of the neck cells. 

 When these cells are directly above the center of the oosphere, 

 the sperm-nucleus comes into contact with the upper part of the 

 egg-nucleus (figs. 214, 217, 218, 221, and 223, a) ; but if the 

 neck be eccentrically placed, the sperm-nucleus will be found 

 against one side of the oosphere nucleus (figs. 216, 219, and 

 220). I have not observed the male nucleus beneath the egg- 

 nucleus as figured by Coulter ('97) in Pinus Laricio. Neither is 

 there a bulging of the egg-nucleus towards the sperm -nucleus, 

 nor do the sexual nuclei ever approximate in size as shown in 

 this same figure of Coulter's, but a somewhat similar figure has 

 been observed in Pinus Strobus after the first division of the 

 "segmentation-nucleus." Schaffner ('96 and '97) also notes a 

 bulging of the nucleus of the oosphere towards the male nucleus 

 in Alisma and in Sagittaria> but, as will be shown presently, 

 the exact converse of this is true in the pines which I have 

 investigated. The sperm-nucleus is usually described as being 

 more dense than the egg-nucleus at the time of their conjuga- 

 tion, and I have sometimes found this to be the case in Pinus; 



