22 



PLANT EELATIONS. 



general oiitline of such a plant, therefore, is usually not 

 conical, as in ■ the other case, but cylindrical (sre Figs. 4, 

 15, 16, 22, 15, So, 90, 155, 102, 160 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 mucli-branclied leaves and palm-Uke habit. 



observation in this direction, and serve to show that the 

 arrangement of h'uves in reference to light depends upon 

 many things, and is by no jiieans a fixed and indifferent 

 thing. The study of any growing plant in reference to this 

 one relation presents a multitude of proldems to those who 

 know how to observe. 



B. On liorizinilul stems. 



23. Examples of horizontal stems, that is, stems exposed 

 on one side to the ilirect light, will be found in tlic case of 

 many branches of trees, stems prostrate on the ground, and 



