132 BOTANICAL GAZETTE [AUGUST 
more vigorous, as does a group of cells that lies just above the 
pedicel, and which projects into the sporangial cavity (fig. 58). 
This cushion is in close relation to the vascular strand and prob- 
ably facilitates the supply of nutriment to the sporangium wall, 
until the embryos begin to form. 
Frequently I have found microspores (in which the sper- 
matozoids had formed) within the megasporangium at the period 
of fertilization, and it is possible that the microspores are hurled 
into a gaping megasporangium when ejected from the micro- 
sporangium.? This is rendered more probable by the frequent 
occurrence of microspores caught in the angles between spor- 
ophylls and stem. Moreover, if plants that have become some- 
what dry be profusely watered, the mature microsporangia open 
explosively and discharge spores. 
Mrcrospores.— The microspores of S. aus are much smaller 
than those of S. Kraussiana and S. Martensii. They early develop 
a pebbled, thick exospore, which causes much trouble in imbed- 
ding and sectioning (fig. 69). Moreover, a comparatively small 
number, in proportion to the immense output, mature. Curious 
aberrations in growth are constantly found. It was necessary to 
study mature gametophytes discharging spermatozoids and trace 
back the different stages to the mother cells. Frequent com- 
parative measurements finally afforded a clew to detecting abnor- 
malities in the early stages. 
Not more than five sixths of the potential mother cells 
divide into spores; the others rapidly disappear. The division 
is accomplished in a manner analogous to the division of the 
megaspore mother cell, which is very little larger. Two spore 
coats develop, a thick spiny exospore, and the delicate mem- 
branaceous endospore. The microspores are shaped like the 
tI have examined S. Martensii, S. Kraussiana, and S. denticulata, growing in 
the greenhouse, with reference to this point. The two former do not shed their 
strobili, and I have found loose megaspores containing sporophytes in the soil on the 
enches where the plants are growing. The last mentioned species, on the other 
hand, sheds its strobili in profusion. I find, however, that their spores are invariably 
sterile and aborted, and therefore am unable to form an opinion as to whether this 
shedding is the normal habit, or due to cultivation in an unnatural environment. 
