6 BOTANICAL GAZETTE [JULY 
The connecting fibers of the first spindle produce a distinct 
cell-plate, extending entirely across the cell before the nuclei 
have begun to divide a second time. -On each side of the plate 
the starch grains are densely crowded. The chromosomes of the 
second division are single slightly curved rods, and are evi- 
dently of about the same size as the halves of the double chro- 
mosomes of the first division. The starch begins to disappear 
during the second division of the pollen mother-cell, and is com- 
pletely used up during the formation of the exine of the pollen 
grains, which becomes quite evident in about three days after 
the last division. The nucleus of the fully formed but yet 
undivided pollen grain is evenly and coarsely granular and gen- 
erally without a nucleolus (fg. 8). 
About ten days after its formation the pollen grain divides. 
The spindle is very small and the chromosomes are propor- 
tionately longer than in the reducing division (figs. g and 70). 
This is the only division of the pollen grain, no sterile prothal- 
lial cell being formed, and it separates at once the generative 
cell from the tube cell. The former is flattened lens-shaped, 
concave toward the inside, and furnished with a distinct //aut- 
schicht ( fig. 11). This division occurs a few days before the 
pollen is shed, and it is in this condition that the ripe pollen 
reaches the nucellus (fig. 72). In the absence of any sterile 
prothallial cells, Taxodium agrees with the Capresseat and 
Taxus, and differs from all other conifers and’ “cycads. The 
number of sterile prothallial cells in the pollen grain of gym- 
nosperms has been determined in the following cases: two in 
Ginkgo (Strasburger, ’92), Larix europaea (Strasburger, 84), Picea 
vulgaris ( Belajeff, 93), Pinus silvestris (Strasburger, ’92), Pinus 
Pumilio (Coulter and Chamberlain, O01); one in Ceratozamia 
(Juranyi, 82; he occasionally found two in C.. longifolia), Zamia 
(Webber, ’97), Cycas (Ikeno, ’99); none in Biota, Cupressus, 
Juniperus (Strasburger, ‘02h Taxus baccata and Juniperus ( Bela- 
jeff, ’93). 
The great importance of correctly determining the number 
of divisions in the pollen grain has not been overlooked, and 
repeated sections, at all stages of the development of the pollen 
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rs pretence 
