128 
/. C. Th. Uphof. 
Summary. 
About six per cent of the known species of Selaginella are 
xerophytic. Their geographical distribution is closely associated 
with that of xerophytic ferns. 
Comparing various species of xerophytic and hygrophytic 
Selaginellas one notices the very close proximity of the dorsal and 
ventral leaves in the former and the great distance between the 
succeeding leaves in most species of the latter. There is a striking 
similarity in the size of the leaves of all xerophytic species, while 
in all hygrophytic Selaginellas there is a great difference in the 
size of dorsal and ventral leaves. This similarity in size of leaves 
of xerophytic forms is of much importance from the photosynthetic 
standpoint; the ventral leaves produced under the influence of this 
Fig. XI. Selaginella Pvinglei, 1, epidermis and hypodermis. S. imbricata, 2 and 
3, opposite sides of lower part of the stem, showing epidermis and hypodermis, 
both have cells with thin walls ; 4, section of middle portion of stem ; 5, part 
of lower half of the stem ; 6 uppermost, and 7, lower surface of the stem 
above the middle. Note difference in thickness of cell walls of the uppermost 
part and lower part of the stem. 
extreme environment contain but few chloroplasts, and most of 
the production of organic matter has to take place in the 
comparatively large dorsal leaves. 
There are three groups of xerophytic Selaginellas. (1) Plants 
with vertical leaves, of the same shape and size. The apex of each 
leaf ends in a long awn containing no chloroplasts. The anatomical 
construction is sclerotic. (2) Plants having slender, wiry trailing 
stems, spreading over the ground or hanging from rocks and 
sometimes trees. (3) Plants having a spreading habit, stems often 
forming a flat, dense and close rosette, rolling into a cluster-ball 
during drought. 
