Igor ] SPORANG/JA AND GAMETOPHYTES OF SELAGINELLA 183 
unshed and the sporangia are still attached to the strobilus. At 
this period the strobilus ceases to form new sporangia. The 
strobilus of S. rupestris retains its physiological connection with 
the plant until the embryo has produced cotyledons and a root. 
15. In the early autumn S. apus sheds all strobili whether fer- 
tilization has occurred or not. S. rupestris retains its stroblii 
throughout the winter and fertilization occurs in the spring. 
16. S. apus forms twelve to fifteen megasporangia in each 
strobilus, all of whose spores are generally fertile. The com- 
paratively limited number of embryos formed is due probably 
either to the limited number of fertile microspores, or to 
mechanical! difficulties in the way of fertilization, possibly both. 
S. rupestris produces strobili far in excess of the number of 
purely vegetative branches, the majority of which develop only 
sterile spores except under very favorable conditions. The 
sterile spores are shed profusely during the summer, and the 
strobili which remain on the plant throughout the winter retain 
their power of apical growth. The first sporangia formed in the 
early spring contain microspores. There is but a limited number 
of these ; then follows under favorable conditions either fertiliza- 
tion or the development of megasporangia, which continues 
until checked by the development of embryos in the older 
regions of the strobilus, or in case fertilization fails by the 
approach of winter. 
TECHNIQUE. 
The tender tips of the strobili offer no special difficulties in 
preparation for the microtome, but the older sporangia, espe- 
cially the closely compacted strobili of S. rupestris, are exceed- 
ingly resistent to the entrance of reagents, and the hardened 
epidermis of the sporophyll, combined with the thick walls of 
sporangia and spores, render sectioning difficult. Certain stages 
of the spores are peculiarly liable to collapse. These technical 
difficulties probably explain many gaps in our knowledge. The 
following method was followed in preparing the material for 
this investigation. 
