Physiological Anatomy of Xerophytic Selaginellas. 127 
hygrophytic species nor xerophytic plants grown in a moist 
environment produce oil; the main product of C,H, and O is 
starch which is, however, less present in xerophytic plants grown 
in exposed places. This suggests that oil is a protection as well 
as a reserve food. Dead cells, like those of certain parts of the 
thick-walled cortex and especially of the hypodermis possess very 
large drops of oil, which frequently occupy the entire width of the 
cell. 
Fig. X. Selaginella Pringlei , 1, ventral leaf ; 2, dorsal leaf. Selaginella 
lepidophylla, 3, ventral leaf. 
The writer’s study of the behaviour of xerophytic Selaginellas 
leaves many questions unanswered, among which the structure 
and action of the roots and rhizophores is of first importance, as 
is also a comparative study of osmotic pressure in cells of plants 
grown in the desert and in a moist atmosphere; further the 
development of the gametophyte and a closer study of photo¬ 
synthesis have to be considered. Satisfactory results can only be 
obtained when plants are studied in their natural environment, 
