110 
J. C. Th. uphof. 
the xylem, because the water supply has increased; although they 
are never as wide as those of hygrophytic Selaginellas. The 
difference in size of the elements of the phloem is not considerably 
marked. A section of the leaf (Fig. Ill, 2), shows a somewhat 
thinner cuticle ; the stomata, which also only appear in the groove 
on the aligular face, are present in larger number, their guard 
cells are covered by a thinner cuticle ; although the external air 
chamber remains. The sclerotic cells are not as numerous, and 
not as thick. The cells of the mesophyll are slightly larger and 
have broader air spaces between them; those toward the stomata 
are considerably larger. 
Fig. IV. Selaginella arenicola, section of stem. 
Treatment with KOH shows that all the thick-walled tissues 
are heavily suberized in those plants grown in exposed places. The 
yellow color is not as intense in tissues of plants grown in the 
moist environment of the greenhouse, which suggests a less amount 
of suberine in the secondary walls. The awns and the wings of the 
leaves, composed of sclerotic cells, are suberised. 
