212 Nichols, A morpkological study of Juniperus communis var. depressa. 
Pollination. 
At the time of pollination tlie micropyle of the ovule is wide 
open (fig. 1), and “from each orifice tliere is exuded a minute 
globule of clear, shining liquid which rests like an irridescent bubble 
on the tip ? and serves to catch the pollen and conduct it to the 
nucellus within” (Jack 1893). Here the microspores usually lodge 
in the irregulär, sancer-shaped depression produced by the partial 
breaking down of the superficial cells of the nucellus, and within 
a few days the micropylar canal is almost completely closed by 
the growth of the inner layer of cells of the integument at the 
region near the tip of the ovule (fig. 2). Noren (1907) is of the 
opinion that this closure is incited by the entrance of the pollen, 
and he finds that in cases where extraneous pollen is present, but 
none of Juniperus , the micropyle remains open, an Observation 
which the writer can confirm. 
The male gametophyte. 
Development of the pollen tube. — As first noted by 
Hofmeister (1851), a little over twelve months elapses between 
pollination and fertilization. A similar prolonged period of growth 
is characteristic of the male gametophyte in Pinus and Cephalo- 
taxus, but in the majority of Gymnosperms, among them Juniperus 
virginiana, only a few weeks or months intervene between polli¬ 
nation and fertilization. Sludsky (1905) maintains that in J. 
communis also the development of the male gametophyte is com- 
pleted in a single season, but the investigations of Noren (1907) 
and of the writer prove conclusively that this is not the case. 
In the material studied, no microspores were found which 
showed the primary nucleus in the act of dividing. This division 
takes place within a week after the pollen reaches the nucellus 
and results in two nuclei slightly different in size from one another, 
the smaller of which — the generative nucleus — immediately 
becomes invested with a dense layer of cytoplasm and is separated 
from the protoplasm of the cell by a thin plasma membrane or 
‘Hautschicht’. Soon after this division the exine of the microspore 
is ruptured, usually on the side toward the nucellus, and the intine 
is pressed outward (figs. 40, 41). The growth of the pollen tube 
proceeds rather slowly throughout the summer months and then 
ceases altogether until the following spring. Düring this period 
of activity the tube presses into the tissue in the upper part of 
the nucellus, disorganizing the cells with which it comes in contact, 
and branches somewhat, thus anchoring itself firmly (figs. 42, 43). 
Frequently the tube wanders across the top of the nucellus before 
penetrating it, and in many cases, after forcing its way into the 
nucellar tissue, the tube turns sharply and grows for some distance 
in a horizontal direction. Düring the first season’s growth the 
vegetative nucleus occupies a Position a short distance from the 
growing end of the tube, while the generative cell lies close against 
