114 MARGARET C. FERGUSON 



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

 nucl3i but he was unable to demonstrate the fact. There can be 

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

 Frius (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, a.) 

 Union of the Sexual Nuclei. — There is ever}'- 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, ci)\ 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 Pimis Sh'ohus 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; 



