Division of the Generative Nucleus in Pines . 201 
only the vegetative nucleus and this pollen-grain signifies 
little, for those who have studied the pollen-tube of Pinus 
know that it is the exception rather than the rule when a 
given pollen-tube can be traced through the lacerated dead 
tissue of the upper portion of the nucellus to the pollen-grain 
from which it proceeded. Such a condition as that just 
described is rarely met with at so late a date. But occasionally 
during the summer and fall pollen-grains are found in which 
no cell-division has taken place since pollination, although 
in the majority of cases the stalk- and the generative cell 
have already been formed. These observations seem to 
indicate that, while the division of the antheridial cell takes 
place comparatively soon after the pollen-grain has germi- 
nated in Pinus Strobus and P. austriaca (other species have 
not been studied with regard to this point), it may under 
certain conditions be much delayed, and in some cases, 
doubtless, never takes place at all. This question can only 
be decided by actual observation of the mitotic figure at 
different periods of the year. Meanwhile, we know that in 
Pinus Strobus and P. austriaca at least, the stalk- and the 
generative cell are formed as a rule before the approach of 
winter. At first these two cells are very similar, but the 
generative cell soon increases somewhat in size (Figs. 10 
and 11). 
A vertical section of an ovule collected on Jan. 4 is 
represented in Fig. 2. The spongy tissue surrounds a cavity 
crossed by irregular strands of protoplasm in which the free 
nuclei of the prothallium are embedded. The stalk and the 
generative cell are enclosed within the pollen-grain, and 
the vegetative nucleus is near the apex of the irregularly 
branched pollen-tube. This pollen-tube is shown more 
highly magnified in Fig. 12. At this time the pollen-tubes 
have penetrated the nucellus almost to the point at which it 
joins the free limb of the integument. The greatest depth 
to which the tubes may have grown is not indicated in the 
illustration. The section was figured because it shows most 
clearly the cells of the pollen-grain and tube. Other sections 
