Fertilization in Pinus S trod us. 
4.67 
Summary. 
The time at which the archegonia appear, in the species of 
Pinus which I have studied, varies somewhat, but in general 
they can first be detected about two weeks before fertilization. 
They are normally found at the micropylar end of the pro- 
thallium, and arise by the differentiation of certain of the 
peripheral cells. By the later growth of the female gameto- 
phyte, the mature egg is sunk to a considerable depth in the 
prothallial tissue, but there always remains an open channel 
leading from the neck-cells to the nucellar cap. The number 
of archegonia varies in the different species from one to nine. 
When the number of oospheres formed is small, they are almost 
spherical in outline ; but this shape may be greatly modified 
according to the number and arrangement of the archegonia. 
In Pinus Strobus , the typical neck of the archegonium 
consists of four cells, all lying in the same plane, while in 
Pinus austriaca and P. rigida it is made up of eight, disposed 
in two layers of four cells each ; but there is a lack of uniformity 
both in the number and in the arrangement of these cells, not 
only in different, but in the same species. 
The central cell is very vacuolate at first, its nucleus always 
remains close beneath the neck-cells, and is more or less 
concave on the side toward those cells. When the ventral 
canal-cell is cut off, about a week before fertilization, the 
vacuoles have nearly disappeared from the venter of the 
archegonium. 
The spindle in the division of the central cell arises as 
a multipolar diarch one, and lies wholly within the nucleus. 
That portion of the mitotic figure which gives rise to the 
ventral canal-cell varies much in the later stages of its develop- 
ment ; but, whatever irregularity characterizes the upper part 
of this spindle, it always becomes monopolar, or nearly so, at 
its lower, inner extremity. 
The form and structure of the nucleus of the ventral canal- 
cell are very variable, and are correlated with the irregularities 
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