408 Lawson .— The Ganietophytes and 
which I interpret to be the archesporium. In the early stages of the 
group, that is when it consists of four or eight cells, the individual cells appear 
to be exactly alike, being quite large with dense granular cytoplasm and 
deeply staining nuclei, and stand out in sharp contrast to the surrounding 
smaller sterile cells. About this time, however, the most centrally situated 
cell of the young archesporial group enlarges and becomes differentiated 
into a functional megaspore-mother-cell. This cell not only differs from 
the other archesporial cells by its large size, but also by the presence of 
numerous starch grains in its cytoplasm which were not found in any of 
its neighbours. These facts are well brought out in the longitudinal section 
of the sporangium represented in Fig. 15. Here it will be seen that the 
mother-cell lies in the centre of a large group of sporogenous cells located 
deep in the tissue of the nucellus. 
It should be noted that the form of the sporangium is unusual. The 
ovules being quite numerous, they become crowded and closely packed 
together. The nucellus consequently takes on a flattened form, its breadth 
in transverse section being just about twice its width, as may be seen in 
Fig. 14. Another interesting point is brought out in this figure, namely, 
that the insertion of the integument is not at the same level around the 
base of the nucellus. This insertion is much higher up, at the narrower 
side of the flattened nucellus. This arrangement obviously gives strength 
to that region of the nucellus in which the sporogenous tissue is developing. 
I have not observed this in any other coniferous ovule. 
As above stated, there is but a single functional megaspore-mother¬ 
cell differentiated out of the sporogenous group. There was no evidence 
to show that its origin was any different from that of the other archesporial 
cells which surround it. And although the latter continue their merismatic 
activity for some time, there is no reason to regard them as other than 
sporogenous. They eventually develop into a large group of nourishing 
tapetal cells which completely surrounds the megaspore. This group of 
cells is, therefore, as in Pseudotsnga (Lawson, ’ 09 ), tapetal in function and 
archesporial in origin. It persists for about a year, but is finally absorbed 
at the time of the formation of the permanent prothallial tissue. 
I was fortunate enough to obtain a fairly complete series of stages 
showing all the essential points in connexion with the reduction division of 
the megaspore-mother-cell. In the first place, this cell is easily detected 
by its large size, by the presence of starch grains in its cytoplasm, and by 
its relatively large and deeply staining nucleus. The latter body, even in 
the resting stage, is much larger than any of the tapetal nuclei. The chro¬ 
matin in the resting condition consists of delicate threads which interlace 
with one another, giving the appearance of a reticulum. There is always 
present at least one large nucleolus. As division approaches, the chro¬ 
matin threads become more sharply defined, and what appeared to be 
