62 MARGARET C. FERGUSON 



The endosperm has become a solid mass of tissue at the time 

 when the generative nucleus divides. The archegonia are still 

 comparatively small and quite vacuolate and the central cell has 

 not yet divided (fig. 72, plate VI). 



Grozvth of the Sperm-nuclei. — After the mitotic figure has 

 entirely disappeared, the sperm-nuclei are separated by a con- 

 siderable distance. The form assumed by the cytoplasm sur- 

 rounding them seems to vary with the shape of the pollen-tube. 

 Gradually the two nuclei approach each other until they come 

 to lie in the extreme uppermost part of their cytoplasm (figs. 112, 

 plate X, 117, 118, plate XI). There is now considerable differ- 

 ence in their size. This inequality in size could be detected as 

 far back as the formation of the daughter-nuclei (figs. 109, no, 

 plate X). Belajeff ('91) was the first to figure and describe bi- 

 nucleated sperm-cells in the Gymnosperms. Coulter and Cham- 

 berlain ('01), page 94, cite Belajeff as having observed an unequal 

 division of the generative cell in Taxtis^ the larger male cell func- 

 tioning, the smaller one remaining in the tube. But if I translate 

 the German correctly, what Belajeff says is that the nucleus of 

 the generative cell divides forming two nuclei which are about 

 one-half as large as the nucleus from which they were derived ; 

 one nucleus becomes larger and occupies a central position in 

 the plasma, the other nucleus is flattened and remains at the 

 periphery of the cell on its upper side ; the flattened nucleus 

 was never found surrounded by its own plasma, but in the same 

 plasma with the spherical nucleus. This is exactly the condi- 

 tion shown in Belajeff's figures, one of which is reproduced by 

 Coulter and Chamberlain. Jager ('99), however, has shown 

 two dissimilar sperm-cells in Taxus, the larger one in advance, 

 but he finds that occasionally the nucleus of the smaller cell 

 may exceed in volume that of the larger one. Jaccard ('94) 

 found two sperm-nuclei of the same size in Ephedra both sur- 

 rounded by the same mass of cytoplasm, and Coker ('02) has re- 

 cently described the sperm-cell in Podocarpus as binucleated, the 

 smaller nucleus being above the larger and " thrust almost out 

 of the cell." No one, I believe, except the writer (1901''""'^), 

 has recorded the presence of a single binucleated sperm- 

 cell in the AbietinecB. In his earlier studies of the Gymno- 



