360 



The Living Plant 



cell divisions become more active at definite points near its base, 

 and push out flat projections which develop and grow into the 

 leaves, as shown by our accompanying figure 137, and diagram- 

 matically by figure 139, C. Unlike new roots, the leaves have their 

 places of origin determined not by stimuli from without, but by 

 internal influences, for they come out from the bud in accordance 



Fig. 137. — A bud (of Elodea, a water plant), in surface view and section, showing unusually 

 clearly the mode of development of new leaves. (Copied from a wall diagram by 

 L. Kny). 



with definite mathematical systems, as we have considered already 

 under phyllotaxy (page 62). In their early stages, and while 

 their tissues are still young, the leaves are flattened closely over 

 one another into the conical structure we commonly call a bud; 

 but as they become old enough to be useful they bend outward 

 and ultimately present their inner faces to the sun. As they grow, 

 their blades tend to take horizontal positions under guidance of 

 gravitation, but they are easily swung therefrom, and given 



