Germination of Forest Trees 



69 



next greatest in the loam. In the case of Pinus ponderosa clearly 

 the greatest length is either in the loam or in the gravel and the 

 shortest length of stem is in the sand. Loam and gravel are, as 

 we have seen, quite opposite when it comes to moisture retentive- 

 ness, hence the good development of plants grown in gravel must 

 be attributed to other properties of gravel, namely, the amount 



The Effect of Soil Texture upon Stem and Root Development 



Conifers 



of air in the soil. Pinus strobus shows the greatest height growth 

 in the sand. Robinia shows the greatest length of stem in the 

 loam and the least in the gravel. This is in peculiar contrast to 

 Pinus ponderosa. For growth Robinia is evidently more par- 

 ticular about soil moisture than about the amount of air in the 

 soil. Quercus rubra shows the greatest height growth in the 

 loam and the least in the gravel. 



The tap root of Pinus ponderosa is of greatest length in the 

 gravel and least in the loam, and the total length of lateral roots 

 is greatest in the gravel. This naturally follows from the fact 

 that, as has been pointed out before, gravel allows water to 

 percolate rapidly and the top layers dry out very soon, hence the 



