246 BOTANICAL GAZETTE ; [ APRIL 
losing their power of division, enter upon a period of growth 
which is quite comparable to that occurring in vegetative meri- 
stems. The difference in size of the sporangia represented by 
Jigs. 43 and 63, which are drawn under the same magnification, 
is due partly, it is true, to increase of the number of cells, but a 
glance at the two figures shows there has been also a decided 
growth of the individual cells. | 
Accompanying the modification of the trabecular cells, there 
is a change of form of their nuclei. These become first elon- 
gated and oval (fig. 50), and finally spindle-shaped, suggestive 
of the changes which attend the development of the vascular 
strand out of the tissues of a growing point. Instances of much 
greater elongation than that shown in fig. 57 are frequently met 
with, though in other cases the changes are comparatively slight. 
The nuclei at this time are relatively large and prominent, and 
appear to form the center of aggregation of what little cytoplasm 
still remains in the trabecular cells. In old sporangia the cells of 
the trabecule are nearly or quite empty, and much compressed. 
Bower has discussed the function of the trabecule. They 
may serve for mechanical support of the sporangium, or to afford 
a larger nutritive surface, or, since the two functions are not 
incompatible, for both. The relation of the trabecule to the 
base of the sporangium where it is closest to the vascular bun- 
dle, and the resemblance of the nuclei to those of plerome regions 
in general, suggested to me that the trabeculae might be the chan- 
nels through which nutriment is supplied to the spores ; but the 
suggestion is not borne out by observation. It is clear that ina 
hydrophytic plant no elaborate apparatus is needed to provide 
the sporangium with water, which can easily enter directly from 
the outside; and an examination of my sections shows that 
the organized food stuffs, such as starch and oil, pass to the 
spores through the inner wall of the sporangium, and not through 
the trabecule. 
The tapetum, as already stated, is organized out of that layer 
of the sterile cells, whether of wall or trabecule, which is in contact 
with the fertile cells. Ata stage between those shown in figs. 48 
