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1907] SMITH—TRUNK AND M1ICROSPORANGIUM OF CYCADS 1 95 
being larger than the surrounding cells and in an axial position (fig. 
22); this cell is the archesporium. In sections parallel to the surface 
of the sporophyll this same cell can be distinguished from the surround- 
ing cells (fig. 25), so that it is evident that it is the single archesporial 
cell which GorBEL (11) predicted in reviewing TrEeuB’s work. 
TREvB (8) failed to find in Zamia muricata less than four sporo- 
genous cells, and LANG (16) concluded that the corresponding four 
cells in Stangeria represented the archesporium, which was “ prob- 
ably not a single cell.” The archesporial cell divides usually by an 
anticlinal wall (fig. 23), and the two daughter cells lie side by side 
in a cross-section through the sporophyll; one cell is often larger 
than the other and divides earlier (jig. 24). 
Occasionally the archesporial cell divides by a periclinal wall 
(jig. 26), suggesting the statement of Bower (15) in reference to 
Angiopteris, in which the divisions are not always in the same direction 
in different sporangia. This exceptional division is shown.also in a 
section parallel to the surface of the sporophyll (jig. 27). 
The second division is anticlinal also, resulting in a hypodermal 
plate of four cells, only two of which are seen in cross-section. 
The third division is periclinal, resulting in an outer and inner 
plate of four cells each (jig. 24), the outer plate being the primary 
wall cells, the inner plate the primary sporogenous cells. Further 
divisions of the sporogenous tissue are shown in jigs. 28—3o. 
The wall is four to seven layers of cells in thickness, always thicker 
at the angles and in the region of the apex (jigs. 31, 32); there is 
some small increase in the number of layers toward the center of 
the sorus also. The cells of the two layers adjacent to the tapetum 
are narrow and flattened (fig. 33), and later are crushed by the develop- 
ment of the sporogenous cells and the activity of the tapetum. The 
epidermal cells are thin-walled in Ceratozamia and Zamia up to the 
time of tetrad formation. At this time in Zamia they begin to show 
thickening along the crest of the sporangia, where the cells are deeper 
and narrower. Here the inner and vertical walls become thicker 
(fig. 32), so that by the time spores are formed these cells make a well- 
defined band along the crest of the sporangium; at the time the spores 
are ready to be shed this wall has become very thick. The new 
layers of the wall fill the cell until the lumen almost disappears. The 
