112 SEEDING AND PLANTING 



sion and final explosion of the seed under the action of heat will 

 not occur when it is overdry. This test is so simple in application 

 that it is often practiced when time will not permit other methods. 

 Seed that has lost its viability through overdrying and later has 

 reabsorbed the lost water behaves in this test like fresh seed. 



22. THE DETERMINATION OF VIABILITY BY GERMINATION TESTS 



The true viability of seed can be determined only through physio- 

 logical investigations, namely, by the germination of an average 

 sample. In most European countries, forest tree seed is subjected 

 to standard germination tests before it is placed on the market. 

 The results of these tests are known to the buyer when the seed 

 is purchased and serve as a basis for the sale. For the most part, 

 the tests are made at government seed-control stations, equipped 

 for germinating seed on a large scale under the perfect control of 

 air, heat, light, and moisture. When the test is made but a short 

 time prior to the purchase of the seed, the purchaser has accurate 

 knowledge of the percentage of germination that he may expect. 



Forest tree seed is usually sold in the United States without a 

 guarantee of germination. Because of the large financial loss that 

 invariably results from delayed or poor germination, it is particu- 

 larly important, therefore, that the purchaser subject it to germi- 

 nation tests before sowing. Germination is the chief factor in 

 determining the density of seeding both in nursery practice and in 

 direct seeding. 



It is found in practice that it is quite impossible to select from a 

 given lot of seed duplicate samples that arc exactly alike. Even 

 were it possible to select uniform samples, they would not give 

 uniform germination values because the conditions under which 

 germination proceeds can seldom be made absolutely uniform. 

 Bates 1 describes a series of tests made at the Fremont Forest 

 Experiment Station with ten samples of western yellow pine seed 

 carefully selected from the same lot. The tests were made in soil 

 and conducted with the usual care. At the end of 25 days the 

 germination scored from 44.2 per cent to 72.4 per cent. The 

 difference in germination was due to the difficulty in securing aver- 

 age samples and uniform conditions for germination. The utmost 

 care must be exercised in the selection of the samples for testing and 



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

 vol. VIII, p. 128. 1913.) 



