se a Bia 
eer ity CAPa Wy =O ae dE Ey 
1903] GAMETOPHYTES AND EMBRYO OF TAXODIUM 7 
from the mother-cell stage to the sprouting of the pollen tube, 
have been made from collections obtained in both 1900 and 1901, 
and I think it certain that there is but one division of the pollen 
cell in Taxodium. | 
— THE POLLEN TUBE. 
The first indication of sprouting is given by the swelling up 
of the generative cell into the tube cell, and by an increase in 
size of both nuclei (fig. 73). The exine is usually thrown off 
at an early stage, as shown in fig. zg. In this figure the nuclei 
of the pollen tube have not changed their position, the tube 
nucleus lying immediately above the generative cell. The pol- 
len tube contains no starch, either now or during its course to 
the prothallium. As the tube advances, the tube nucleus moves 
from its position over the generative cell and passes slowly down 
toward the tip. Indications of branching are soon seen in the 
pollen tube (jigs. 17, 29, 22, 23). In fig. 76 the generative cell 
seems by its position to be bounded by an actual membrane, 
but no indication of a cellulose wall was obtained, and if one is 
present it is exceedingly thin and quickly dissolved. By com- 
paring figs. 75 and 76 it will be seen that the sprouting does not 
take place at any definite point in reference to the position of 
the generative cell. 
The division of the generative cell does not occur until sev- 
eral weeks after the sprouting of the grain (figs. 19-21). The 
stalk nucleus soon loses its definite hold upon the protoplasm 
around it, although immediately after the division (fig. 79) it is 
" still bounded by a distinct protoplasmic sheath. The central cell 
retains the characteristics which mark the generative cell before 
division. It is furnished with a distinct Hautschicht and has the 
Shape of a double convex lens. It will be noticed that imme- 
diately after the division the stalk cell is larger than the central 
cell. Belajeff (’91, ’93) describes these two cells as being of 
€qual size in Taxus. In Juniperus communis he (’93) finds the 
outer cell to B& smaller, while in Picea vulgaris the opposite is 
true. There is not much difference in size in Pinus Laricto, as 
figured by Coulter and Chamberlain (grt). It will thus be seen 
that Taxodium agrees with Juniperus in the relative size of the 
stalk and central cells immediately after their formation. 
