22 
PLANT STUDIES 
general outline of such a plant, therefore, is usually not 
conical, as in the other case, but cylindrical (see Figs. 4, 
15, 16, 22, 45, 83, 96, 161, 174, 178 for branched leaves). 
Many other factors enter into the light-relation of foli- 
age leaves upon erect stems, but those given may suggest 
FIG. 16. A cycad, showing much-branched leaves and palm-like habit. 
observation in this direction, and serve to show that the 
arrangement of leaves in reference to light depends upon 
many things, and is by no means a fixed and indifferent 
thing. The study of any growing plant in reference to this 
one relation presents a multitude of problems to those who 
know how to observe. 
B. On horizontal stems 
23. Examples of horizontal stems, that is, stems exposed 
on one side to the direct light, will be found in the case of 
many branches of trees, stems prostrate on the ground, and 
