10 MARGARET C. FERGUSON 



plasm filled with metaplasm. In the pines, a large vacuole 

 often held several smaller ones. The egg-nucleus slowly filled 

 itself with metaplasm during its descent to the center of the 

 cell. Three successive divisions occurred in the large cell of 

 the pollen-grain in Lartx, the first two prothallial cells formed 

 were small and soon disorganized, the third one increased greatly 

 in size and divided to form the stalk- and the body-cell. 



It was left for Belajeff (1891) to establish the true nature of 

 the cell-complex found in the pollen-grain of the Gymnosperms. 

 He demonstrated the fact that in Taxus baccata the large nucleus 

 of the pollen-grain is the vegetative or pollen-tube-nucleus, as 

 in the Angiosperms, and that the sperm-nuclei arise by the 

 division of one of the smaller cells of the pollen-grain, this 

 smaller cell first dividing to form the stalk- and the generative 

 cell. 



Strasburger (1892) showed that Belajeff 's observations on the 

 structure of the pollen-grain and the development of the pollen- 

 tube in Taxus baccata were, in general, true for the other 

 Gymnosperms. He described the mature pollen-grain in Pinus 

 as containing a large tube-cell, a small cell the third prothallial 

 or antheridial cell and the remnants of the first two prothallial 

 cells. Pollination was immediately followed by the germination 

 of the pollen-grain, and the nucleus of the large cell wandered at 

 once into the tube. The last formed prothallial cell remained in 

 its place in the pollen-grain until the following spring, when it 

 divided into the stalk- and the body-cell of the antheridium. 

 The division of this cell was not studied, but Strasburger 

 thought it took place at about the same time as the develop- 

 ment of the archegonia. The pollen-grain of Picea was found 

 to correspond exactly with that of Pinus excepting that the an- 

 theridial cell divided while still within the anther. The sperm- 

 cells in Pinus were seen in the apex of the pollen-tube ; the 

 lower cell was the larger ; and each cell was almost entirely 

 filled with its large, coarsely granular nucleus. At the tip of 

 the pollen-tube, the stalk- and the tube-nucleus could no longer 

 be distinguished one from the other. The sperm-nucleus was 

 shown to be smaller than the egg-nucleus, but the two were 

 alike in the amount of active nuclear substance ; and attention 



