22 



PLAXT RELATIONS. 



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, 155, 162, 174 tor 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 



