Physiological Anatomy of Xerophytic Selaginellas. Ill 
Selaginella arenicola , a psammophilous species, collected from a 
dry, sandy pinewood near Dappatah, Florida, shows a similar 
anatomical construction, the hypodermis, however, is thicker along 
certain radii of the stem, giving an irregular star-shaped form on a 
cross section (Fig. IV), on the other hand the stem of 5. rupestris 
has a square, sometimes a five-angled shape. Old cell walls which 
were very exposed are impregnated with a red-brown pigment, which, 
no doubt, serves as a protection against very intense light. The 
vascular bundle of the stem shows the same characteristics as in 
5. rupestris, S. rupincola and S. densa. A cross section of the leaf 
shows a far more developed sclerenchyma than in the species 
previously described (Fig. V, 1). The stomata, which also appear on 
the aligular surface, are protected by stiff one-celled hairs. On a 
longitudinal section of the leaf (Fig. V, 6), one notices the thick- 
walled elongated cells of the sclerenchyma. The mesophyll 
contains larger inter-cellular species than in the species previously 
described ; it is composed of roundish cells toward the upper surface, 
lower down they are elongated. 
A section of the leaf of 5. rupincola (Fig. V, 7) is of much the 
same structure as 5. rupestris . The vascular bundles in the leaves 
of all species mentioned under Group I, are best developed near the 
base and occupy only a small portion of the centre of the leaf. 
The bundles are usually composed of four narrow tracheids, which 
are narrower than those of plants developed in a moist situation. 
Around the xylem are some parenchyma cells and a few sieve tubes, 
which do not show any differences in plants grown in various 
environments. 
Group II. 
Plants belonging to this group have a flat, spreading habit and 
have slender stems which are as a rule widely branched, and wholly 
or partly covered with small, sometimes scale-like, leaves. Some 
species show resemblances to the third group, as they are able to roll 
up during drought, but do not form a nest-ball, since they are 
too widely branched. One of the principal representatives is 
5. sanguinolenta . The plant examined was collected in a rocky 
mountainous situation in Kurram Valley, Afghanistan. The stem 
is very thin, spreading and pinnately branched ; and the branches 
frequently sub-divided again ; these divisions are short and covered 
with very small scale-like leaves (Fig. I, 6) all of the same size and 
shape. This species is supposed to stand near the borderline of the 
heterophyllous and homophyllous Selaginellas. These leaves are 
