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, 7. 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 Pinus ponderosa the 
tap root is 2%4 times longer, in Robima 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 : 
Tue Errect oF Soil Moisture UPON STEM AND Root DEVELOPMENT 
Conifers and Hardwoods 
Stem Measurements Root Measurements ? 
o A fe P , Gh. R. 
Wesrecs Pinus ponderosa| Robinia pseud. Resse P. pon era 
2 Mos., | 3 Mos.,| 2 Mos., | 3 Mos.,| 2 Mos.,| Tap, Wate. Tap, 
Cm. Cm. Cm. Cm. Cm. Cm. Cm. Cm. 
IDA Sco aieotcrera Gta eens ue bile 208 2.60 BES ies oF oe 6.004 
Ie Gana es es es eich sce ee 1.80 | DOP | ABS | BILBO || Sow || wes |) BOR | aby! 
VE Se oe eae nce 2.76 | 2.59 | 6.00 | 7.02 | 4.31 | 5.03 | 1-11 | 9.64 - 
3 Age, 3 months. 
4 Age, 2 months. 
