The Profound Effect on the Structure of Plants 57 



Third, the conditions to 

 which are adjusted the round 

 and the linear shapes of 

 leaves are uncommon in 

 comparison with that in 

 which numerous leaves are 

 spaced at different heights 

 along ascending stems, 

 for this latter is the prevail- 

 ing mode in vegetation, 

 (figure 12, right). Since this 



leaves. These symmetri- II I 111 condition is intermediate 

 cal cone-shaped trees may I between the other two, we 



be viewed, indeed, as a se- I anticipate an intermediate 



ries of superposed meadows, I shape of leaf, which would 



spaced well apart in stories 1 1 1 1 therefore be elliptical in out- 



so arranged that each is 

 smaller than the one next 

 beneath it, thus avoiding 

 injurious shading thereof, 

 while the leaves point out- 

 ward as well as upward to- 

 wards the strongest light. 

 This condition is repre- 

 sented diagrammatically in 

 figure 14, and it comes very 

 close to actual realization 

 in some of our Spruces and 

 Firs when these are free to 

 develop as they will (figure 

 15). * This is the principal 

 factor, I believe, in the ex- 

 planation of the conical 

 form of the evergreens. 



FIG. 13. Conventionalizations of the three fundamental types of leaf form. 



