CHAPTER XL. 



FOLIAGE LEAVES. 



I. General Form and Arrangement of Leaves. 



746. Influence of foliage leaves on the form of the stem. 



The marked effect which foliage has upon the aspect of the plant 

 or upon the landscape is evident to all observers. Perhaps it is 

 usual to look upon the stem as having been developed for the 

 display of the foliage without taking into account the possibility 

 that the foliage may have a great influence upon the form or 

 habit of the stem. It is very evident, however, that the foliage 

 exercises a great influence on the form of the stem. For ex- 

 ample, as trees increase in age and size, the development of 

 branches on the interior ceases and some of those already formed 

 die, since the dense foliage on the periphery of the trees cuts 

 off the necessary light stimulus. The tree, therefore, possesses 

 fewer branches and a more open interior. In the forest also, 

 the dense foliage above makes possible the shapely, clean timber 

 trunks. Note certain trees where by accident, or by design, the 

 terminal foliage-bearing branches have been removed that foliage- 

 bearing branches may arise in the interior of the tree system. 



Without foliage leaves the stems of green plants would develop 

 a very different habit from what they do. This development 

 could take place in three different directions under the influence 

 of light: (i) The light stimulus would induce profuse branch- 

 ing, so that there would be many small branches. (2) The stem 

 would develop fewer branches, but they would be flattened. 

 (3) Massive trunks with but few or no branches. In fact, all 



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