132 SEEDING AND PLANTING 



used in field operations, as conditions become unfavorable for 

 germination because of lack of moisture. In field practice germi- 

 nation depends upon the amount and distribution of the precipi- 

 tation. It does not depend upon how wet the soil becomes at times 

 but how long it remains sufficiently moist to induce germination. 

 Even in nursery practice where suitable moisture conditions can 

 be maintained by irrigation, the delayed germination is crowded 

 out by the earlier, more vigorous plants or attacked by damping- 

 off fungi. For these reasons it is becoming more and more the 

 practice to base utilization value entirely upon germinative energy. 



37. Germination Values as Compared with Tree Per Cent 



Recent investigations show that the percentage of germination 

 obtained by standard germination tests is not proportional to the 

 percentage of plants obtained in actual field or nursery practice. 

 Seed having a germinative capacity of 70 will not produce seven- 

 ninths as many plants as seed having a germinative capacity of 

 90 but only about half as many. The tree per cent lags behind 

 the germinative capacity, and the lower the capacity the greater the 

 divergence. Haack 1 first pointed out this principle and proved 

 its importance in determining the value of seed for nursery and 

 field seeding. He found with Scotch pine that the plant per cent 

 from seed with different germinative capacities was as follows: 



In the above table 85 is accepted as the average germinative 

 capacity for fresh Scotch pine seed. Seed with this germinative 

 capacity gave a plant pep cent of 31. Applying this in practice 

 with seed having different germinative capacities, it appears that 

 2.2 times as much seed should be used when the germinative 

 capacity is but 65 and but 0.7 as much'when the germinative capac- 

 ity is 95. In other words, were it necessary to use 5 pounds of seed 

 per acre having a germinative capacity of 85, it would be neces- 

 sary to use 11 pounds of 65, 7 pounds of 75, and but 3| pounds 

 of 95 in order to obtain the same plant per cent. These and other 

 more recent experiments prove that low-grade seed is much less 



1 Haack, Oberforster: Der Kiefernsamen. (Zeitschrift f. Forst- u. Jagd- 

 wesen, S. 353-381. 1909.) 



