336 BOTANICAL GAZETTE [NOVEMBER 
formation of the pollen chamber is easily seen. The middle lamella 
softens and breaks down, thus setting free a few cells which are soon 
resorbed, and so forming the beginning of a pollen chamber. The_ 
subsequent encroachment of the disintegrating region is most rapid 
downward, but is also increasingly extensive at the periphery, so that 
the completed chamber is more or less funnel-shaped. 
Below the free portion of the nucellus its most. conspicuous feature 
is the thick jacket which surrounds the endosperm (fig. 11, ej). This 
jacket is sharply differentiated from the rest of the nucellus, and is so 
tenacious that it can be stripped off with forceps. The megaspore- 
membrane sometimes adheres to it, but more often clings to the 
endosperm. Although the material contained no early stages in the 
formation of the jacket, it is evident that it originates as a layer only 
one cell in thickness. Where cells of the layer do not divide peri- 
clinally, it remains only one cell thick; if there is a single periclinal 
division, the layer becomes two cells thick; while another division 
would make it three cells in thickness. In the archegonial region a 
considerable portion of the cells undergo one periclinal division; 
while in the chalazal region nearly all the cells show such a division, 
and a large number undergo a second periclinal division. On the 
sides there is a gradation between these two extremes. The less 
prominent and less complete jackets of the Coniferales have been 
described by THoMSoN (21). 
The cells of the jacket are very frequently binucleate and occa- - 
sionally three nuclei are found. In comparison with the size of the 
cell these nuclei are rather large, but their chromatin content is very 
scanty and the nucleoli are small (fig. r2). It is not at all uncommon 
in these cells to find a complete chromatic spirem lying perfectly free 
in the cytoplasm, with no trace of a nuclear membrane or any achro- 
matic structures (fig. 13). In such cases the nucleolus is always 
present and is somewhat larger than that of resting nuclei. The 
amount of chromatin in the spirem is vastly greater than in the resting 
nuclei. This unique condition does not lead to the formation of 
daughter nuclei or even to the reorganization of the single nucleus, 
and the significance of the phenomenon is not evident. The cells of 
the jacket at this time are centers of extreme metabolic activity, 
all the materials for the nutrition of the rapidly growing endospe™™ 
