LIFE HISTORY OF PINUS 



9 



most of the two sperm-nuclei in the pollen-tube which is instru- 

 mental in effecting fertilization. He reported the presence of 

 an axial row of three cells in Larix, the lowest cell being the 

 embryo-sac-mother-cell. The generalization was made that 

 the prothallium arises in all the gymnosperms through free 

 cell-division, all the free nuclei dividing at the same time. It 

 was claimed that but a single endosperm was formed in the 

 Abietinea, that the primary nucleus of the embryo-sac remained 

 undivided during the first year, and that the " transitory endo- 

 sperm " of Hofmeister was in reality the freed cells of the nucel- 

 lus which were destined to be absorbed. It was to these cells 

 that the term spongy tissue was applied. In the following year 

 (1880) Strasburger described and figured the mature archego- 

 nium in Picea and discussed the early stages of endosperm for- 

 mation in Pinus, but he gave little that was new at that time. 

 It was in this same year that Sokolowa (1880) published the 

 results of her researches in the development of the prothallium 

 in the gymnosperms. Cell-walls were laid down between the 

 nuclei imbedded in the peripheral layer of protoplasm, but no 

 cell thus formed was furnished with a wall on its inner free side. 

 These open cells were termed " alveoli." They grew in length 

 until the middle of the embryo-sac was reached, then walls 

 arose at the inner ends and the alveoli were closed ; cell divis- 

 ions followed, and gradually the elongated alveoli gave place 

 to many cells. 



Goroschankin (1880 and '83) reported that the protoplasm of 

 the egg and of the sheath-cells was in immediate contact through 

 pores in the separating membrane ; he saw (i883 2 ) the two 

 sperm-nuclei pass into the egg in Pinus Pumilio^ and believed 

 that both fused with its nucleus ; the great similarity which 

 the spheres in the egg bear to nuclei was commented upon and 

 he questioned the propriety of calling them vacuoles. Stras- 

 burger (1884) confirmed Goroschankin's observations as to the 

 passage of the two sperm-nuclei from the pollen-tube into the 

 egg, but pointed out that only the one in advance fused with the 

 egg-nucleus. As the protoplasmic contents of the central cell 

 increased, the vacuoles decreased, and every transition could be 

 traced between the large vacuoles and the meshes of the proto- 



Proc. Wash. Acad. Sci., July, 1904. 



OF 



