FOREST TREE SEED AND SEED COLLECTING 113 



in securing the greatest possible uniformity in the tests. Tests 

 made by one method should not be compared with tests made by 

 other methods, as they are not likely to be uniform. 



The United States Forest Service has established uniform ger- 

 mination tests in order to determine the germination values of all 

 seed used on the National Forests. 1 These tests are made at the 

 National Forest Experiment Stations and at Washington. 



Germination tests should always be made in duplicate. When 

 the results of the duplicate tests vary 15 per cent or more, they 

 should be repeated. When the tests vary less than 15 per cent, 

 the average of the two should be used in determining germination 

 values. The tests should be made as late as possible before the 

 seed is required for sowing, because the later the time the more 

 closely will the germination approximate that obtained in the field. 



In all methods of testing the germination of tree seed, three 

 conditions must be fulfilled. The seed must be supplied with 

 adequate heat, moisture, and oxygen. Species appear to differ in 

 their requirements for light during germination. With most species 

 a temperature between 60 and 80 F. is most favorable; the mois- 

 ture should not be hi the form of free water about the seed; and 

 the air should be admitted in sufficient quantity to supply the 

 necessary oxygen and permit the escape of carbon dioxide. 



23. Kinds of Germinating Apparatus. Many kinds of 

 germinating apparatus for testing tree seed have been devised. 

 All kinds, however, depend for their effectiveness upon the con- 

 trol of heat, moisture, air and light, and the cost and labor of 

 operation. Any apparatus which will meet these requirements 

 will serve for germination tests. Haack 2 states that for all spe- 

 cies that germinate within 3 or 4 weeks no special apparatus is 

 essential although some forms are preferable to others. 



All methods for testing the viability of tree seed by germina- 

 tion tests may be placed in the following two classes: 



a. The use of soil as a medium through which air, moisture, 

 and heat are brought to the seed. 



6. The use of some medium other than soil through which 

 air, moisture, and heat are brought to the seed. 



1 Cox, W. T.: Reforestation on the national forests. (U. S. Forest Service, 

 Bui. 98. 1911.) 



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

 Jagdwesen, S. 353-381. 1909.) 



