138 BOTANICAL GAZETTE [AUGUST 
the sporangium (fig. zor). The sporophyll immediately above 
it starts simultaneously from an exactly similar cell. A wall 
separates the archesporial cell into an epidermal cap cell anda 
hypodermal cell (fig. 102). The sporangium wall develops 
from the former, the sporogenous tissue from the latter. A few 
sporogenous cells near the base originate from the stem tissue 
(fig. 105). 
The tapetum and sporangium development are quite like 
those of S. apus. The sporophylls and stem apex, on the other 
hand, have no apical cell. The ligule appears later in the his- 
tory of the sporophyll than in S. apws, and the megaspore mother 
cell is somewhat larger. Certain cytological features serve to 
distinguish these cells from the sterile sporogenous cells (jig- 
106). The division into spores presents some curious varia- 
tions. Sometimes the spore mother cell divides once only, form- 
ing two megaspores; again, after the first division, one of the 
daughter nuclei may divide, or occasionally both. In any case, 
so far as observed, but one or two normal megaspores are ever 
formed; if there are others, they are dwarfed in size and never 
grow. That the exospore is a membrane common to both spores is. 
evident from figs. zz9, 720, r2z. The forthation of the mesospore 
and endospore is not preceded by any such deeply staining layer 
as is represented in fig.42. The protoplasmic vesicle expands 
and overtakes the spore wall. This stage terminates the develop- 
ment of the megaspore (fig. 723). Inthe older sporangia, nearer 
the base of the strobilus in the specimens that I examined, no 
further development had occurred beyond increase in size and. 
thickness of the spore coats—the contents showed that the 
spores were abnormal. 
This sequence of events, although followed step by step: 
repeatedly, had been rejected as probably not normal, until the 
sporophytes were discovered. As the number and shape of the 
megaspores in these sporangia which contained embryos agree 
with the stages described, in spite of the gap that remains to be. 
bridged between the megaspore and mature gametophyte, itseems. 
reasonable that the observations can be relied upon as far as 
