Division of the Generative Nucleus in Pines. 203 
tube has increased little, if at all, in length, renewed activity 
in the male gametophyte being first indicated by a further 
development of the cells still within the pollen-grain. 
The stalk-cell increases in size and its cytoplasm assumes 
a vacuolate character. The growth of the generative cell is 
still more marked, and its cytoplasm on the contrary becomes 
dense and deeply staining. (Compare Fig. 12, Jan. 4, with 
Fig. 13, May 3.) In Pinus sylvestris , as studied by Dixon, 
the generative cell divides while it is within the pollen-grain. 
In the species of pines which I have investigated, this division 
does not occur until the generative and the stalk-cell have 
entered the pollen-tube, and the stalk-cell has passed below 
the generative cell. As the generative cell increases in size 
it stretches out towards and into the neck of the pollen-tube, 
drawing after it the stalk-cell, or possibly being forced out 
by this cell, the two passing into the tube together. Dixon 
states that only the naked nucleus of the stalk-cell enters 
the pollen-tube, and in so far as I am aware, no writer has 
described the entrance of the entire stalk-cell into the pollen- 
tube in the Abietineae. The material which I have studied 
shows conclusively that the nucleus does not ‘ slip out ’ of its 
cytoplasm (Figs. 12-15). The entire cell can be identified 
in the tube and later in the egg. During the time that this 
cell is moving over the generative cell its cytoplasm cannot 
always be clearly differentiated from that of the latter ; but 
when once the stalk-cell has passed the generative cell, its 
nucleus surrounded by a sphere of very vacuolate cytoplasm, 
scarcely more than a peripheral layer, is again distinctly 
demonstrated. After passing the generative nucleus, the 
stalk-cell ordinarily takes up a position between the gene- 
rative cell and the vegetative nucleus (Plate XIII, Fig. 21); 
occasionally it may pass the vegetative nucleus (Fig. 22). 
When the generative cell leaves the pollen-grain, its nucleus 
is situated near the top of the cell, but it apparently moves 
faster than does the accompanying cytoplasm, and when the 
stalk-cell passes the generative nucleus, this nucleus lies at 
or below the centre of its cell (Figs. 13, 19, and 20). Shortly 
