Morphology of Cycadean Sporangia . 427 
of the archesporial cells in the pollen-sac of an Angiosperm, 
while the outer segments correspond to the primary tapetal 
cells. 
The first division in the sporogenous cells is by a periclinal 
wall, so that a group of four cells is seen in a vertical section 
(Fig. 7). Since four sporogenous cells are visible in transverse 
sections of sporangia of this age (Fig. 8) it is clear that there 
is a cubical group of eight cells. The cells surrounding each 
sporogenous group keep pace with its increase in size and 
undergo frequent divisions. At the central point of the sorus 
and between the developing sporangia the hypodermal cells 
soon lose their merismatic character and cease to grow, so 
that the sporangia become distinct from one another. In such 
cases as that shown in Fig. 4, growth has not been arrested in 
the interval between the sporangia of each pair, but these 
also become free from one another at a later stage. The stalk 
of the sporangium is derived from the growth of the tissue 
beneath the sporogenous group. 
After the stage represented in Fig. 7 has been reached, the 
divisions in the sporogenous cells do not follow in exactly the 
same order in different sporangia. Usually each of the upper 
cells is divided by anticlinal walls, and the resulting cells 
undergo periclinal divisions. From the lower of the shaded 
cells seen in Fig. 7 the greater part of the sporogenous 
tissue originates : these cells divide, in the more regular 
examples, into four by periclinal and anticlinal walls. The 
subsequent divisions of these cells occur in various directions, 
but the position of the earlier division walls remains traceable 
for some time (Figs. 9, 10). In transverse section the whole 
of the sporogenous mass can as a rule be referred to the group 
of four cells present in similar sections of younger sporangia 
(Fig. n). 
The shape of the sporogenous group differs to a consider- 
able extent in sporangia of the same age, as will be seen on 
comparing Figs. 9 and 10. These differences stand in relation 
with the general form of the sporangium, which appears to be 
influenced in no small degree by the pressure to which it is 
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