FOREST TREE SEED AND SEED COLLECTING 111 



its characteristic color and appearance of freshness, and the em- 

 bryo is likely to shrivel and only partially fill the cavity. 



It is the common practice to estimate the viability of many 

 seeds by the cutting test alone. This is particularly true of large 

 seed, such as walnut, hickory, oak, chestnut, maple, ash, and those 

 that require a long time to germinate as illustrated in cherry, 

 tulip, hornbeam, and black gum. Large seeds as in oak and 

 hickory are usually buried in damp sand for 30 days before testing. 

 Smaller seeds are soaked in water until the kernel is saturated. 



A large percentage of the seed that appears good under ocular 

 examination fails to grow when subjected to germination tests. 

 Experiments with 40 species at the Yale School of Forestry ex- 

 tending over a period of 10 years gave results that averaged much 

 higher than those later obtained from germination tests. With the 

 broadleaved, large-seeded species such as walnut, oak, hickory, 

 maple, and ash, the results from cutting tests compared most 

 favorably with those obtained later by germination tests, but even 

 here they were much too high. The ocular examination of the seed 

 of coniferous species and small-seeded, broadleaved species gives re- 

 sults that are often 50 per cent higher than those obtained from germi- 

 nation tests. In some instances this is due to the fact that 

 overdried seeds, those that have been subjected to excessive heat 

 in their removal from the fruit and those that have lost their 

 vitality by long storage, are not detected by direct examination. 



The cutting test is useful in supplementing germination tests 

 of coniferous and other small-seeded species. Thus when the 

 germination test is completed, the ungerminated seed should be cut 

 open and a record made of those that are apparently viable but 

 which for one reason or another have failed to germinate during 

 the period allotted to the test. 



21. THE DETERMINATION OF VIABILITY BY PHYSICAL TESTS 



The moisture content of seed is often indicative of viability. 

 Fresh seed always contains considerable moisture. Overdrying in 

 removing the seed from the fruit or from long storage in a dry at- 

 mosphere may reduce the moisture content below that of viable 

 seed. A simple test for moisture content may be made as follows: 

 Place an average sample upon a hot plate or shovel. The mois- 

 ture within the seed, as it becomes heated, expands causing the 

 seed to puff up and finally explode and spring away. The expan- 



