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parenchyma, which is thicker and here and there contains large 
air spaces. Although the anatomical construction of the stem of 
S. pilifera and S. lepidophylla differ but slightly, the leaves of the 
latter possess more elongated cells in the mesophyll. In S. 
Pringlei , the cells of the hypodermis and cortex also are similar 
(Fig. XI, 1) to those of 5. pilifera , but there are 5 to 7 rows of cells 
in 5. pilifera and 5. lepidophylla from 7 to 9. Other species, e.g., 
5. involvens , 5. longispicata, and S. convoluta possess the same 
characteristics as S. pilifera. There is, however, one striking 
difference in 5. imhricata ; specimens of which from Arabia, 
Zambesia and Abyssinia were examined. Individuals do not form 
fiat, dense rosettes, like the other species of this group ; the stems 
are more or less erect; the lower part is not branched but only 
covered with a few scale-like leaves (Fig. XI, 5). The upper half of 
the stem is branched as in other species. The various tissues are 
here similar to S. pilifera. The almost leafless and thick stem, is 
very hard and the cells are extremely thick-walled ; the cells of the 
epidermis are smaller than those of the hypodermis. There is no 
difference in size between the cells of the hypodermis and most 
cell layers of the outer cortex ; toward the centre the inner cortex 
becomes thin-walled (Fig. XI, 4). All the cells contain a large 
amount of oil; especially those of the thin-walled cortex. The cell 
walls of both sides of the lower stem are of the same thickness 
(Fig. XI, 2, 3) in all tissues. In the upper half of the stem, which is 
much branched and covered with both kinds of leaves, there is a 
marked difference in thickness in cell walls (fig. XI, 6, 7) between 
the upper and lower surfaces of each branch, as has been described 
in S. pilifera and 5. lepidophylla. 
Comparing the xerophytic Selaginellas of Group II and III 
with the hygrophytic species, it is apparent that the same tissues 
are present in all plants, although in modified form, corresponding 
with their particular environments. Xerophytic species adapt 
themselves easily to very moist and shaded environment; on the 
other hand, hygrophytic species are unable to grow in semi-arid 
situations. 
A striking difference between plants of two different 
environments is that all the elements of xylem are much wider in 
hygrophytic than in xerophytic plants, and this feature stands in 
close relation to the water supply of the plants; moreover 
xerophytic species which have grown in a moist atmosphere have a 
more pronounced proto- and metaxylem. The cel** of the cortex 
