Physiological Anatomy of Xerophytic Selaginellas. 117 
part of the underside of a ventral leaf; (a) being very much 
exposed to the sun’s rays has a red-brown color; (b) which was 
less exposed is white and glossy, both (a) and (b) reflecting the 
light; (c) remains green having been deeply shaded by a part of 
the next leaf, and possesses living protoplasm. A cross section of 
the leaf shows that none of the tissues under (a) and (b) contain 
any chloroplasts, only some grayish bodies in the cells which may 
indicate their presence at an earlier stage of development; very 
young leaves which are developed during the rainy season are 
Fig. VII. Section of stem of Selaginella pilifeva from moist and shady 
greenhouse. Note difference of cell walls of upper and lower surface. 
entirely green. These chloroplasts must have been destroyed by 
the intense light; thus if parts of leaves which shade green 
portions of the succeeding leaf are removed, after a short time the 
exposed parts also become colorless and soon light reflecting. 
Leaves of plants developed in a moist and shaded greenhouse 
are entirely green, with the exception of two rows of cells on the 
margin which are colorless. 
Moreover the writer found on desert plants which are very 
much exposed that the underside is covered with a hard translucent 
