164 Lawson . — The Gametophytes and Embryo of 
represented in PL XII, Fig. 1. Within the spore two degenerating prothallial 
cells, lying close to the spore-wall (p\ p ") were readily recognized. One of 
these appears as a mere film of deeply-staining nuclear substance, closely 
applied to the inner surface of the spore wall, while the other is represented 
by a small irregular mass of chromatin situated close to its neighbour but 
in a line towards the interior of the spore. The presence of these pro- 
thallial cells in the pollen grains, in which there are no bladder-like 
swellings of the exine to afford buoyancy, does not give support to the 
view (Robertson, ’ 04 ) that a correlation exists between the survival of 
the prothallial cells and the winged character of the pollen. 
In addition to the two prothallial cells, there are two large free 
nuclei within the microspore. One of these is centrally situated and is 
the so-called generative nucleus; the other is the tube nucleus. Both 
nuclei are surrounded by dense granular cytoplasm, and between the 
latter and the spore wall are numerous starch grains. As indicated in 
Fig. 1 all four nuclear structures lie in the same plane ; that is in a row 
one behind the other. 
The pollen-receiving device in Pseudotsuga is quite peculiar and un- 
like anything yet described for Gymnosperms. For some little time after 
pollination, the nucellus presents the form of a small protuberance with 
a perfectly rounded apex. The integument extends for a considerable 
distance beyond the nucellus. At a point immediately above the apex of 
the nucellus the integument bends inward in such a fashion as to partly 
close or narrow the micropylar canal, and then sharply bends outward 
again. This results in the formation of a distinct stricture midway between 
the apex of the nucellus and the mouth of the mieropyle. As a result of 
this peculiar curvature of the integument, the micropylar canal is not 
a straight passage of uniform width, but consists of two chambers, one 
immediately above the apex of the nucellus, and the other near the mouth 
of the mycropyle. The relative position and form of these two chambers 
are shown in Fig. 3, as well as the narrowness of the passage between 
them. The fact is also made clear in this figure that the curvature of 
the integument is much greater on the side nearest the ovuliferous scale. 
In addition to this narrowing in the middle region of the mieropyle, 
the integument is still further modified. It will be seen in Fig. 3 that the 
extremity of the integument which forms the mouth of the mieropyle is 
folded inward. On the inner surface of this infolding extremity numerous 
fine hair-like processes are present. A close examination of these pro- 
cesses made it clear that they were not cellular in structure, but were 
merely outgrowths from the external walls of the epidermal cells. They 
serve very effectively, however, as a stigmatic surface, for during pollination 
the extremity of the integument is directed outw T ard instead of inward. 
It will be remembered that in nearly all of the Coniferales the pollen 
