404 Lawson .— The Gametophytes and 
fact that the sections here represented are not median. The inner membrane, 
seen in transverse section, is in reality quite thin. The microspores them¬ 
selves are not exactly spherical in form, they are slightly elongated or 
egg-shaped. At one end of the long axis the exospore becomes sharply 
attenuated, and at the end of the spore it is very thin. This peculiarity of 
the spore-wall is indicated in Figs. 2, 3, and 4. 
The contents of the mature spore consist of a large centrally placed 
nucleus suspended in a rather dense granular cytoplasm, as shown in Fig. 1. 
The stage here figured is one just preceding the germination of the spore, 
for its nucleus is obviously preparing for mitosis. In Fig. 2 is represented 
the first spindle in the germinating microspore, the chromosomes being at 
the equatorial plate. Fig. 3 represents a later stage with the chromosomes 
at the poles of the spindle. It will be observed from Figs. 2 and 3 that 
the long axis of the spindle is parallel with the long axis of the spore, and 
consequently one of the cells resulting from this division will find itself 
placed directly behind the weak spot in the spore-wall. The result of this 
first division of the germinating spore is represented in Fig. 4. The 
daughter-nuclei are seen to be separated from one another by a delicate 
membrane, so that there are now two cells organized. 
This division of the microspore takes place within the microsporangium, 
and it is the only division which occurs before pollination. In fact no 
other divisions occur until the pollen-tube is formed. Unlike the Abietineae 
(Coulter and Chamberlain, ’ 01 ; Ferguson, ’ 04 ; Lawson, ’ 09 ) and Podocarpus 
(Coker, ’ 02 ), there is not a trace of vestigial prothallial cells, and therefore 
the two cells that are formed are to be regarded as the generative cell and 
tube-cell respectively. At the time of pollination the pollen-grain is in the 
condition represented in Fig. 4. The grain is slightly oval in form, with 
the tube-cell in touch with the thin part of the exospore. 
The young ovules, among the Coniferales, show a considerable variety 
of special adaptations in the form of devices for receiving the wind-con¬ 
veyed pollen. In many of the Cupressineae which I have observed, the 
micropyle, at the time of pollination, exudes a small globule of trans¬ 
parent liquid. The purpose of this is no doubt to catch the pollen more 
effectively, and as the liquid evaporates the pollen-grains descend into the 
micropyle and find themselves lodged upon the apex of the nucellus. 
I have observed practically the same thing in Cephalotaxus and Taxus. In 
Pimts the integument of the young ovule extends outwards in the form of 
two free limbs which, upon receiving the pollen, curve towards one another, 
and the grains are thus led into the micropylar canal. In Pseudotsuga 
(Lawson, ’ 09 ), on the other hand, the pollen-grains are caught in the 
stigmatic surface of hair-like structures at the lip of the micropyle, and 
here they germinate, sending down the pollen-tubes through the micropylar 
canal. The grains themselves in this case never reach the nucellus. In 
