FOREST TREE SEED AND SEED COLLECTING 131 



This method for calculating utilization value has been in use for 

 many years. At best, however, it is but a crude approximation 

 of the actual number of plants that should be expected in nursery 

 or field practice. It is far too high. 



Utilization value based upon germinative energy is now recog- 

 nized as more fully expressing the real value of the seed, hence the 

 desirability of employing it in an expression to represent utiliza- 

 tion value. In the introduction of this factor into the formula 

 for utilization value the following equation is used: 



purity X germinative energy 



Utilization value = 



100 



In a sample of western yellow pine seed having a purity of 97 

 per cent and a germinative energy of 49 per cent in 20 days, the 

 utilization value is as follows: 



TT , .,. , - 97 X 49 



Utilization value = ^: = 47.5. 



Both germinative energy and germinative capacity are sometimes 

 introduced into the formula for utilization value. Under this 

 interpretation of utilization value the formula is as follows: 



purity X g er - ener gy + ger. capacity 

 Utilization value = 



100 



In a sample of western yellow pine seed having a purity of 97 

 per cent, germinative energy of 49 per cent in 20 days, and a 

 germinative capacity of 84 per cent, the utilization value is ex- 

 pressed as follows : 



97 X 



Utilization value = - rrr - = 64.5. 



Bates, 1 in developing the seed-testing investigations for the 

 Central Rocky Mountain Region where the favorable period for 

 germination is usually short, assumed that only those seeds which 

 germinate very vigorously under hothouse tests are useful under 

 field conditions. The delayed germination occurring after the seeds 

 have been under test from 20 to 30 days is useless when they are 



1 Bates, C. G.: The technique of seed testing. (Proc. Soc. Am. For., vol. 

 VIII, p. 134. 1913.) 



