THE FOREST NURSERY 283 



When the seed has an unusually high viability less should be 

 used. When the viability has been reduced by storage or other 

 causes, more seed should be used. 



The author believes that when the viability of the seed is the 

 average for the species, the amounts given in the above table are 

 too high for the best results. In his experience, red pine, jack 

 pine, and arbor-vitse sown at the rate of 6 ounces to 48 square feet 

 of seedbed produce 300 or more seedlings per square foot, which 

 is far too dense for the production of satisfactory stock. 



Schlich 1 recommends the following amount of fresh seed for 

 48 square feet of seedbed when broadcasted: 



Oz. 



Scotch pine 4.4 



Norway spruce 4.4 



Austrian pine 6.4 



European larch 8.0 



21. Formula for Seed Quantity. The following formula ex- 

 presses the amount of seed required for any given area of seedbeds: 



EYN 



S = The quantity of seed in pounds or quarts. 



P = The area of seedbeds in square feet. 



F = The desired density or number of plants per square foot. 



E = The utilization value of the seed. 



Y = A variable factor expressing the relation between tree per 



cent and utilization value. 

 N = The number of seeds per pound or quart. 



The necessity for the factor Y in the above formula is due to 

 tree per cent being far below utilization value based upon germi- 

 native capacity and usually below utilization value based upon 

 germinative energy. Many seeds of weakened vitality germinate 

 but do not develop, others germinate "rump first" and soon 

 wither and die. To what extent tree per cent in the nursery lags 

 behind germination values derived from tests varies with the 

 quality of the seed and to some extent with its size. Old seed 

 in which the vitality has been impaired by storage or fresh seed 

 in which the vitality has been weakened by gathering before ma- 

 turity or by overheating in extracting from the fruit may exhibit 

 a tree per cent 20 per cent or more below the number that germi- 



1 Schlich, Wm.: Manual of forestry. 4th ed., vol. II, p. 210. London, 1910. 



