6 Lawson . — The Gametophytes , Archegonia , Fertilization , 
make their appearance. During this time the trees are constantly en- 
veloped in a cloud of pollen, so that it would be almost impossible for any 
of the exposed ovules to escape the reception of at least a few of the 
grains. At this time the integument of the ovule is about on a level or 
a little above the apex of the nucellus, and from four to six pollen-grains 
are here deposited. The grains remain in this position for three or four 
weeks without further germination, when the integument grows over them 
and closes the micropyle in the manner described by Shaw (1896). 
The first indication of the further germination of the pollen-grains 
was the splitting off of the hard thick wall. (If some ripe grains are 
examined in water under the microscope, it will be seen that the casting 
off of the outer wall takes place suddenly and with considerable force, 
leaving a thin delicate membrane underneath.) The pollen-tubes now 
push out over the tops of the nucellus, and one or two of them may grow 
down between the nucellus and the integument, as shown in Fig. 3. 
Material collected during the first week in March frequently showed the 
pollen-tubes extending more than halfway down the side of the nucellus. 
In such cases the tube-nucleus was invariably near the tip of the tube, 
with the generative nucleus considerably in the rear. Both nuclei were 
found in the central axis of the tube, suspended in a broad strand of 
cytoplasm which contained an abundance of starch grains. 
While one or two of the tubes may follow the course between the 
nucellus and the integument, others may penetrate the nucellus immediately 
at the top, as shown in Fig. 4. The penetration of the tube is accompanied 
by a breaking down and a probable absorption of the cells of the nucellar 
tissue through which the tube forces its way. From a study of longi- 
tudinal and cross-sections in series it became quite evident that the course 
taken by the pollen-tubes may vary considerably. At a later stage cross- 
sections of the endosperm showed the tubes in various positions. Usually 
three or four tubes develop and become functional. In the majority of 
cases they are found situated between the female prothallium and the 
remaining tissue of the nucellus. Many were found partially surrounded 
by endosperm, while others were completely surrounded. In no case was 
I able to find any evidence of branching of the tube, although Shaw 
(1896) reports that 4 quite as often as not it branches.’ 
Just about the time the tube penetrates the wall of the nucellus, the 
generative nucleus, having increased to quite the size of the tube-nucleus, 
divides. As shown in Fig. 4, there are now three nuclei in the tube, one 
large one and the two smaller ones. The largest of these, situated 
nearer the tip of the tube, is no doubt the tube-nucleus, while the other 
two are the stalk- and body-nuclei. Of these latter two there is a slight 
difference in size. As the larger one appears to be preparing for further 
activity, I regard it as the body-nucleus and the smaller one as the stalk- 
