332 Saxton. — Contributions to the Life-history of 
central part of the prothallus, at the time when the archegonia are mature. 
Such cells are fairly frequent in Cupressus at a later stage, but very rare in 
Pinus. I cannot agree with Miss Ferguson ( 7 ) that the formation of such 
cells in Pinus is always delayed to such a late stage as that to which she 
refers, though undoubtedly the first-formed cells are always uninucleate, as 
they are in Callitrineae. From the remarks made by Miyake ( 16 ) in con- 
nexion with Cunninghamia , though he is not very explicit, one concludes 
that binucleate cells are occasionally found in the older prothallus. 
In Sequoia I have not been able to demonstrate such cells at the time 
when archegonia are about mature, but my preparations are not good 
enough to say definitely that they are absent. Lawson ( 14 ) does not 
mention the point. To summarize, the phenomenon is by no means con- 
fined to the Callitrineae, but is more conspicuous in them than in any other 
Pinaceae. In the Taxaceae, as far as known, it is much more prevalent, 
possibly owing in some cases to the small size of the nuclei, as noted in 
preparations of Podocarpus Thunbergii } On the whole, there is no evidence 
that the character is of any importance, except as a nutritive adaptation, 
4. The Male Gametophyte. 
The pollen-grain, as first found in the micropyle, still contains only 
a single nucleus. The thin exine bursts, and starch is no longer found 
surrounding the nucleus. In the example figured (Fig. 24) the grain is 
lodged on the side of the integument, just above the nucellus, but normally 
the pollen becomes attached to the apex of the nucellus. 
The divisions giving rise to the nuclei of the pollen-tube have not 
been seen, the next figure (25) showing a well-organized body cell, and two 
small nuclei, exactly alike in size and structure, embedded in a single mass 
of cytoplasm in advance of the body cell. In this figure one sterile nucleus 
is in advance of the other, but in later stages, until the body cell divides, 
they are almost invariably abreast. The tube takes a somewhat sinuous 
course (Figs. 8 and 25) through the middle of the nucellus, and may 
occasionally branch quite close to the apex. It has not been observed to 
branch in the lower (meristematic) part of the nucellus. The number of 
pollen-tubes growing down the nucellus is commonly two. Their position in 
a transverse section of the nucellus is shown in PI. XXVI, Pig. 26. Sometimes 
three or four pollen-tubes are found. The tubes reach the tip of the 
embryo-sac long before cell formation begins (Fig. 27), and at once grow 
into the prothallial cavity. The pollen-tube and its contents take up 
practically their final position before wall formation begins, though it is 
probable that a very slight amount of growth may occur later. Shortly 
before the body cell divides, the tip of the tube has the structure shown 
1 Miss Gibbs (8), however, figures a case where the nuclei are very large. 
