134 



from 800 to 1,000 seeds should be used. 



Genuineness is determined by com- 

 paring a representative sample of the 

 seed lot under test with samples of 

 known identity. Purity commonly is 

 expressed as the percentage by weight 

 of clean whole seeds true to species in 

 a sample containing seeds and mixed 

 impurities. The number of seeds per 

 pound is obtained by careful weighing 

 of a counted number of seeds. It is 

 usually expressed in two ways: The 

 number of clean seeds per pound of 

 the sample as received and the num- 

 ber of clean seeds per pound of pure 

 seeds. Moisture content usually is ex- 

 pressed as a percentage of the oven- 

 dry weight of the seeds after commer- 

 cial cleaning, but not on a pure seed 

 basis. 



Viability, or the percentage of seeds 

 capable of germinating when exposed 

 to the most favorable conditions, is 

 determined directly by germination 

 tests or indirectly by cutting tests, the 

 growth of excised embryos, flotation, 

 biochemical staining of embryos, or 

 measurements of enzyme activity. The 

 indirect methods give quicker results, 

 but they are seldom as reliable as di- 

 rect germination tests. 



Germination tests usually are made 

 in flats, porous clay pots, or greenhouse 

 benches filled with fine sand, acid peat 

 (sometimes used as compressed mats), 

 or sphagnum moss; or in germinators 

 on porous plates, blotters, filter paper, 

 or agar. Sand, peat, or sphagnum moss 

 are preferred as giving results closer to 

 germination in the nursery. Carefully 

 counted numbers of seeds, pretreated 

 where necessary, are sown on the sur- 

 face of peat mats or at controlled 

 depths in sand, moss, or peat flats. 

 Small seeds are sown shallow; larger 

 seeds deeper, as a rule. 



The sand, peat, or other medium 

 must be kept at a fairly constant mois- 

 ture level. Air temperatures should be 

 controlled closely. Many species ger- 

 minate well at temperatures fluctuat- 

 ing from 68 F. at night to 86 during 

 the day; some do just as well at con- 

 stant temperatures of 70 or 75; 



Yearbook, of Agriculture 1949 



Oak seedling. The two plump seed leaves 

 packed with food remain inside the acorn. 



others need temperatures that fluctu- 

 ate from 50 (night) to 77 (day) ; and 

 some germinate best at temperatures 

 between 40 and 50. The needs of 

 each species must be known and sup- 

 plied for best results. Light is not neces- 

 sary for germination of most tree seeds, 

 but aids that of some southern pines. 

 Germination tests ordinarily are run 

 for 30 to 60 days. Counts should be 

 made every 2 or 3 days, and systematic 

 records of results should be kept and 

 made available to the seed user. 

 Promptness of germination is almost 

 as important to nurserymen as amount. 



NURSERYMEN DETERMINE the rate of 

 sowing from the laboratory tests as 

 modified on the basis of their own ex- 

 perience. Nursery germination of tree 

 seeds commonly is from 50 to 80 per- 

 cent of laboratory germination. Since 



