4 BOTANICAL GAZETTE [JULY 
beginning to disintegrate, the tapetal cells are increasing in size and 
dividing anticlinally, and the mother-cells are in the resting condi- 
tion (February 15, 1903). 
In gymnosperms the number of wall layers varies considerably. 
In Cycadales, Lang (’97) found the wall of Stangeria to consist of 
from three to six layers; in Ginkgoales they number from four to 
seven. Chamberlain (’98) found the wall of Pinus Laricio to be 
almost constantly three-layered. Coker (’02) found three wall layers 
in Podocarpus, the cell-walls of which are very thin and ultimately 
collapse; and in Taxodium he found a single layer. In E. trijurca the 
wall is a single layer of cells, and Strasburger found the same condition — 
in the species studied by him. 
In E. trijurca numerous instances were observed in which indi- 
vidual tapetal cells were not distinguishable from adjacent mother- __ 
cells. This seems to indicate that the tapetum is potentially sporog- 
enous, and by virtue of its position has become sterile. With the 
appearance of the mother-cell the history of the sporophyte ends. 
In general the resting stage of the microspore mother-cell in gym- 
nosperms is long. Chamberlain (’98) observed mother-cells in Pinus 
Laricio, Cupressus Lawsoniana, and Taxus baccata canadensis in 
October. The reduction division occurred about May 1, thus giving 
a resting period of about seven months. In Ephedra the first observed 
reduction division was on March 12, giving a resting period of about 
one month. 
At the time of the reduction division the cells of the wall layer 
are reduced to nuclei, scarcely a trace of cytoplasm being present. 
The cells of the tapetal layer become conspicuously vacuolated and 
their nuclei much enlarged. The nuclei become usually about four 
times the volume of those of the epidermal cells (fig. 7). Two 
or more nuclei are present in many tapetal cells at the time tetrads 
are formed. These last divisions appear to be amitotic, and nuclei 
in all stages, from the dumb-bell stage to complete separation, can 
be seen. At this time the tapetal cells, especially those nearest the 
bottom of the loculi, become enormously distended and very vacuo- 
late (fig. 14). Soon afterwards they become a flattened plate and 
disappear. 
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