140 BOTANICAL GAZETTE [ AUGUST 
possible to make out that they were similar in shape to those of 
S. apus, but much smaller. To each was attached a vesicle. An 
attempt to stain them with osmic acid on the slide failed to 
demonstrate any more details. 
AppENDuM.— Since the foregoing was forwarded for publica- 
tion it has been possible to verify the main facts and to explain 
certain apparently contradictory features with regard to S. rupes- 
tris. The spring and early summer of 1901 were extremely wet 
as compared with those seasons inigoo. S. apus growing in low 
pastures made few strobili and aborted spores in contrast to the 
profusion of the year before, whereas S. rupestris throve in the 
unusual supply of moisture and developed strobili, which in turn 
produced embryos prodigally. The impotency of the mega- 
spores gathered in midsummer of 1900 was obviously due to the 
lack of water; for at the expiration of the rainy season this 
year, the last of June, and before the plants had suffered from 
drouth, they were lifted with all the underlying humus and 
placed in an open situation in the Botanic Garden. Profuse 
watering was continued and thorough draining secured. A 
large percentage of the strobili ripened after fertilization had 
occurred, and instead of few embryos found with much effort as 
in the season of 1900, hundreds of young sporophytes have been 
secured. The sequence of events in a propitious season, based 
upon the observation of two years, seems in brief to be this: 
Strobili are formed on the new vegetative shoots of the plant in 
late summer and autumn. Only megasporangia develop that 
season, and in these the gametophytes reached the stage bear- 
ing archegonia. In the spring, these strobili resume their api- 
cal growth, and first microsporangia appear. Thus each strobi- 
lus has a basal zone of megasporangia approximately six months 
old, and above it a narrow region of microsporangia. The num- 
ber of microsporangia appears to be strictly limited. I have 
found eight to twelve as a rule. Thenceforth so long as the 
strobilus continues to grow during the remainder of that season 
megasporangia only are developed. The production of these 
is checked in case embryos form in the lowermost zone of 
