366 



RELATION TO ENVIRONMENT. 



but the large, wide-spreading leaves at the top of the stem give 



the plant anything but a cylin- 

 drical habit. Some cedars and 

 arbor-vitae are also columnar. 



The advantages of the colum- 

 nar habit of stem are three: (i) 

 That the plant stands above 

 other neighboring ones of equal 

 foliage area and thus is enabled 

 to obtain a more favorable light 

 relation; (2) where large num- 

 bers of plants of the same species 

 are growing close together, they 

 can maintain practically the 

 same habit as where growing 

 alone; (3) the advantage gained 

 by other types in their neighbor- 

 hood in less shading than if the 

 type were spreading. The cyl- 

 indrical type can, therefore, grow 

 between other types with le"s 

 competition for existence. 



716. The cone type. This is 

 well exampled in the larches, 

 spruces, the gingko tree, some 

 of the pines, cedars, and other 

 gymnosperms. In the cone type, 

 the main axis extends through 

 the system of branches like a 

 tall shaft, i.e., the trunk is excur- 

 rent. The lower branches are 

 wide-spreading, and the branches 

 become successively shorter, 

 usually uniformly, as one ascends 

 the stem. The branching is of 



two types: (i) the branches are in false whorls; (2) the branches 



Fig. 422. 

 Cylindrical stem of mullein. 



