Germination of Forest Trees 



65 



The species retained for this work were Pinus ponderosa (S. 

 D.), Robinia pseudocode, Quercus rubra, and Pinus strobus. 

 Stem and root measurements were taken upon the first three of 

 these species and stem measurements only upon the last one. 

 Each measurement represents the average of 10 representative 

 plants, except in case of Quercus rubra where from 3 to 14 

 plants were used depending upon the number available. The 

 measurements of the stems of Pinus ponderosa and Robinia 

 pseudacacia were taken at two different ages, namely at the age 

 of two and three months, but the plants used at the age of three 

 months were not the same ones used at the end of two months. 

 Hence in the data the three months' old plants are not necessarily 

 larger than the two months' old plants, although they usually are. 

 Root measurements of Pinus ponderosa and Robinia pseudacacia 

 were taken at the end of three months. Both stem and root 

 measurements for Quercus rubra were taken at the age of five 

 months. 



The effect of light on stem and root development is shown in 

 the following table : 



The Effect of Light on Stem and Root Development 

 Conifers 



Hardwoods 



