200 Ferguson — Development of the Pollen-tube and the 
then bulges out, the exospore is ruptured, and the endospore 
is gradually prolonged into a tube. Immediately upon the 
formation of the pollen-tube, the vegetative nucleus, as shown 
by Strasburger (’ 92 ), moves away from the antheridial cell 
and towards the tip of the pollen- tube (Figs. 7 and 8). Stras- 
burger (’ 92 ) describes the antheridial cell in Pinus sylvestris 
as remaining unchanged until the archegonia are formed in 
the following spring. Dixon states that it divides about 
a month before fertilization, but from a careful reading of 
the text, one is given the impression that this was an infer- 
ence on his part rather than a demonstrated fact. In some 
species of pines the division of this cell certainly takes place 
very much earlier. During the first week in August there 
have been found on the nucellus, in Pinus Strobus , pollen- 
grains containing two cells (Fig. 10). In such instances the 
vegetative nucleus can invariably be detected in the pollen- 
tube. In the same material, other pollen-grains are observed 
in which the division of the antheridial cell has not yet taken 
place ; but in material fixed somewhat later, it is only rarely 
found undivided. In Pinus austriaca this division also takes 
place during the summer. I once found the mitotic figure for 
the division of the antheridial cell in Pinus resinosa on the 
first of April. As this was the earliest date on which material 
of this species had been collected, I am unable to determine 
at present whether or not it is the normal time for the division 
in Pinus resinosa. 
A pollen-grain with its antheridial cell still undivided has 
been observed just prior to fertilization (Fig. 5). In this case 
two of the three pollen-tubes which have almost reached 
the prothallium are furnished with sperm- and stalk-cells, 
while in the third, only the vegetative nucleus is found. On 
the apex of the nucellus there is a pollen-grain which at this 
late date contains one cell, the antheridial cell, still undivided. 
The nucleus of this pollen-grain (Fig. 5 b) is large, plump, and 
to all appearances perfectly normal, and it is possible, though 
scarcely probable, that it may still divide. That one cannot 
trace a definite connexion between the pollen-tube containing 
