792 Journal of Agricultural Research vol. vi, No. 20 



chamber germination. The differences were insignificant in some cases, 

 but were very large in the field tests of the clovers continued for one year. 

 In this connection the effect of temperatures a few degrees above freez- 

 ing should be emphasized. The laboratory tests in which certain alterna- 

 tions of temperature were used following cool constant temperatures show 

 conclusively that actual freezing is not necessary in order to cause the 

 subsequent softening and germination of many impermeable clover seeds 

 (p. 781). Moreover, in many cases larger percentages of the impermeable 

 seeds softened and germinated in these tests than in any of the tests with 

 seeds which had passed the cold winter months in the soil under the parent 

 plants (p. 781-784). These facts indicate that impermeable clover seeds 

 would germinate as well if sowed several weeks before the beginning of 

 warm weather in the spring as if sowed the preceding fall. In addition, 

 spring sowing would avoid the danger of winter-killing softened seeds or 

 young seedlings. 



USE OF IMPERMEABLE SEEDS 



The value to the farmer of the impermeable seeds occurring in any lot 

 of seed will vary according to the kind of seed, the germinating capacity, 

 the percentage of impermeable seeds in the lot of seed under considera- 

 tion, the age of the seed, and the time of sowing the seed. 



Impermeable alfalfa seed sowed late in the spring is of more value to 

 the crop than impermeable sweet-clover seed sowed at the same time. 



If the percentage of impermeable seed in a given lot is small (10 per 

 cent or less) and the rest of the lot consists of strong, germinable seeds, 

 the impermeable seeds are of little importance both because of their few- 

 ness in comparison with the seeds which germinate readily and because 

 of the varying quantities of seed which are sowed according to common 

 practice. It is when the impermeable seeds constitute a large percentage 

 of the seed in a given lot that their real value becomes a question of agri- 

 cultural importance. 



In seed that is several years old the viability of the permeable seeds 

 may have become so low that the impermeable seeds, which lose their 

 vitality more slowly, are relatively much more important than in lots of 

 fresh, new seeds. 



Impermeable clover seed sowed early in the spring is of more value 

 than the same seed sowed later, when the weather has become settled and 

 warm. 



The following general rules, based upon the experimental results and 

 upon the considerations just outlined, are suggested as guides in agricul- 

 tural practice with the plants investigated. 



Assuming that all seeds have been tested for germinating capacity and percentage 

 of impermeable seeds, calculate the amount of seed to sow as specified below. 



