Igor] SPORANGIA AND GAMETOPHYTES OF SELAGINELLA I41 
megasporangia. Immediately upon the cessation of growth in 
the strobilus and during its ripening, a vegetative lateral bud on 
the axis immediately below the strobilus is stimulated into activity, 
develops horizontal branches, and_roots which grow down into 
the humus. When this new growth is thus made independent, 
the axis bearing the strobilus and the germinating embryos 
decays, and at the period when cotyledons and roots of the young 
sporophytes are thrust out of the sporangia, the strobilus is 
lying in contact with the ground, shaded and otherwise protected 
by the vigorous vegetative growth that is spread above them. 
The strobilus decays much more slowly than the leafy axis 
beneath. This accounts for my finding strobili which appear to 
be shed from the plants. In case a strobilus fails to produce 
embryos, either through failure in fertilization, or probably more 
often because the dry season overtakes the gametophyte at a 
critical stage of its growth, the strobili continue to grow inde- 
terminately throughout the season, and apparently perform 
the vegetative work that, under more auspicious conditions, is 
taken up by the new growth from the lateral bud. Moreover, 
the spores rendered sterile by adverse conditions are shed from 
the sporangia. Thus not infrequently one finds greatly elongated 
strobili with a basal zone of empty gaping sporangia, surmounted 
by two or three whorls of empty microsporangia, then a zone of 
Sprouting embryos, and an apical region of degenerating young 
stages of megasporangia. In contrast with this are the strobili 
which have developed under continuous favorable conditions, in 
which the éasal zone displays embryos. Whether or not the 
strobilus may carry on its growth a third year in case of two suc- 
cessive failures to produce embryos, remains to be demonstrated. 
It will be a matter of interest to discover what variation in eco- 
logical conditions causes the strobili of the allied Texas species 
to pass the winter in a microsporangiate condition, whereas S. 
rupestris in Massachusetts appears to bear during the same sea- 
son only megasporangia. 
THE UNIVERSITY OF CHICAGO. 
[ Zo be continued.]} 
