Division of the Generative Nticleus in Pines . 199 
Pollination. 
In the vicinity of Ithaca pollination takes place in the 
pines during the latter part of May or the first week in June, 
the different species varying a few days. When the pollen- 
grains have been drawn into the depression in the upper part 
of the nucellus, the projecting portions of the integument close 
over them and a resinous substance is secreted which prac- 
tically seals the opening by which the pollen-grains entered 
(Plate XII, Figs. 1 and 7). At this time the pollen-grain 
contains, as described by Strasburger (’ 92 ), the remnants of 
two prothallial cells ; one small cell, the third prothallial cell 
formed, or the antheridial cell ; and a large cell, the vegetative 
or wall-cell (Fig. 6). 
The degree of development which the ovule has attained 
at the time of pollination is shown in Fig. 1. The central 
portion of the nucellus is occupied by an axial row of cells, 
the lowest of which is in the early prophase of division 
(the figure is drawn on too small a scale to show this dis- 
tinctly) ; and the two upper nuclei are in a process of disin- 
tegration, as indicated by their diffuse reaction to stains. 
Frequently only the first cell of the axial row, the macrospore 
of Hofmeister, is present at this time. The so-called spongy 
or loose tissue of Strasburger is already well differentiated 
when pollination takes place. 
The upper concave portion of the nucellus which, together 
with the enveloping integument, forms the pollen-chamber, 
terminates in a row of more or less elongated cells which are 
not closely united at their free extremities, but stand out, 
as it were, like so many fingers to catch the pollen-grains ; 
they also serve to facilitate the entrance of the pollen-tube 
into the tissue of the nucellus (Fig. 7). 
Development of the Pollen-tube. 
The germination of the pollen-grain takes place very soon 
after pollination. The pollen-grain increases slightly in size, 
the concave portion of the wall (^, Fig. 6) becomes convex, 
