Germination of Forest Trees 



67 



The foregoing tables show the effect of soil depth upon root 

 and stem development for the same species and ages of stock. 



In the case of stem development in all species except Quercus 

 rubra, the height of the stem increases with increase in soil depth. 

 The increase in length between the deep soil and the shallow soil 

 is not very great, i. e., in the pines it is never over 0.25 cm. and 

 in Robinia it is never over 1.16 cm. In Quercus rubra the 

 smallest height growth is in the shallow soil but the greatest 

 height growth is in the medium deep soil. It is interesting to 

 note that in all cases the greatest total length of stem and root 

 together is in the plants grown in deep soil. 



As is to be expected the length of the tap root is materially 

 decreased as the soil depth decreases. In Pinns ponderosa the 

 tap root is 2^ times longer, in Robinia it is 5 times longer and 

 in Quercus it is 3 times longer in the case of the deep soil than in 

 the shallow soil. The length of lateral roots was taken only in 

 the case of Pinus ponderosa and this species is representative of 

 what took place in all the other species. In this species the total 

 length of lateral roots increased with decrease in soil depth. In 

 the case of Robinia this is strikingly shown in the photographs. 

 This indicates that whether a tree has deep-seated roots or super- 

 ficial roots depends largely upon the depth of the soil in which 

 the tree grows. The terms " deep-rooted species " and " shallow- 

 rooted species " have therefore only limited significance and the 

 real basis for these terms is in most cases the environment. 



In the following table are given the data upon the effect of soil 

 moisture upon root and stem development : 



The Effect of Soil Moisture upon Stem and Root Development 

 Conifers and Hardwoods 



