Physiological Anatomy of Xerophytic Selaginellas. 105 
rocky situations in Afghanistan and Eastern Siberia; S. mongholica , 
Rupr. from North China; 5, borealis , Spring from Eastern 
Siberia, Kamschatka and Eastern Himalaya; S. saccharata , A. Br. 
from rocky, exposed situations in Mexico. 
Group III. Plants having a spreading habit, stems often 
forming a flat, dense and close rosette; rolling into a nest-ball 
during drought. To this group belong «S. pilifera, A. Br. growing 
in dry, rocky places in Texas, Southern Arizona and various parts 
of Mexico; S. lepidophylla, A. Br. from similar localities in Texas, 
New Mexico, Southern California, and from Mexico to Peru; S, 
Pringlei, Baker, from similar places in Texas and Mexico; *S. convoluta, 
Spring growing in exposed places in tropical America from Mexico 
to Southern Brazil; S. lougispicata, Underw. being reported from 
Yucatan, Mexico; 5, cuspidata, Link.fromCuba, Mexico,Guatemala, 
and Venezuela; 5. imbricata, Spring in semi-arid localities in 
Arabia, Abyssinia and Zambesiland; 5. involvens, Spring from 
similar places in China, Japan, Amurland, Corea, and Eastern 
Himalayas. 
Group I. 
I was able to study 5. rupincola, in its natural state in various 
parts of Southern Arizona (Sabino Canon, Aqua Caliente and 
Oracle near Tucson) and S. rupestris, in Southern Arizona (Sabino 
Canon, near Tucson) Southern California (San Bernardino 
Mountains) and various parts of the Ozark Mountains in South 
Eastern Missouri. Both species are petrophilous, growing mainly 
on exposed cliffs and rock outcrops. Individual plants on northern 
and north eastern exposures are well developed, their stems and 
leaves being greyish green and containing living protoplasm during 
the entire year. The few individuals on hot southern and south¬ 
western exposures are as a rule poorly developed ; during the hot 
spells in summer the stems and leaves are entirely yellow or 
yellow brown, the protoplasm being killed. It is only during the 
rainy season that young shoots appear, which moreover never 
attain the same development as those on plants growing in 
favourable shady situations. Of both species the stems are densely 
tufted, ascending or decumbent; the leaves stand vertically close to 
the stem. They are all alike, sessile and possessing a groove in 
the midrib on the dorsal side; the margins bear one-celled bristles ; 
the apex ends in a long awn and the sporophylls form terminal, 
somewhat four-angled spikes. The first thing one observes about 
5. vupincola is the vertical direction of the leaves, which are 
