66 



Richard H. Bocrkcr 



From these tables it will be seen that Pinus ponderosa increases 

 its length of stem with a decrease in light intensity both at the 

 age of two and at three months. This is likewise true for Pinus 

 strobus. For Robinia pscudacacia, however, both at the age of 

 two and three months, there is a striking decrease in stem height 

 with a decrease in light intensity. Qncrcus rubra behaves the 

 same way, except that the length of stem is greater in the medium 

 shade than in the dense shade. This development is shown very 

 well by the accompanying photographs. 



In the case of all species it is strikingly shown that the length 

 of the tap root and the total length of the laterals decrease with 

 decrease in light intensity. 



In so far as the stem and its relation to light is concerned it 

 is quite evident that hardwoods behave differently from conifers. 

 As has been pointed out conifers tend to increase their height 

 growth with decrease in light intensity while hardwoods tend to 

 decrease this growth with decrease in light intensity. Evidently 

 conifers can adapt themselves to these unfavorable light condi- 

 tions better than hardwoods. In the hardwoods the reciprocal 

 relation of roots and stem in their dependence upon light is strik- 

 ingly shown. 



The Effect of Soil Depth upon Stem and Root Development 

 Conifers 



