68 FORAGE PLANTS AND THEIR CULTURE 



with authentic samples. In other crops, however, special 

 varieties are often indistinguishable by their seeds, so that 

 one must depend upon the reliability or the guarantee 

 of the seedsmen. Among forage crops, mammoth and 

 medium red clover, and Grimm and ordinary alfalfa are 

 examples of varieties indistinguishable by their seeds. 



58. Purity. By the purity of seed is meant its freedom 

 from foreign matter, whether trash, chaff, weed seeds 

 or adulterants. With the exception of perhaps the last- 

 mentioned, impurities are far more common in forage 

 crop seeds than in any others. This is due partly to the 

 fact that most grasses and many legumes are grown 

 broadcasted, and it is rarely possible to keep the fields 

 free from weeds. Furthermore, grass seeds as a rule are 

 light in weight, so that it is difficult to remove chaff, small 

 pieces of straw and the like. 



The impurities that usually occur in each region where 

 seed is largely grown are well known, so that if any others 

 are present, it is strong evidence of adulteration. 



59. Viability. The viability of seed or capacity for 

 germination depends upon many factors, among which 

 are the conditions of the season when grown, the care 

 exercised in harvesting and curing, the manner in which 

 it has been stored, and the age of the seed. 



Viability is tested in laboratories by means of special 

 germinators in which the temperature, moisture, ventila- 

 tion and light can be controlled. The best temperature 

 varies somewhat for the different species. For most 

 grasses the temperatures between 68 degrees and 86 

 degrees Fahrenheit are considered best, and it is found 

 advantageous to use the higher temperature 6 hours and 

 the lower 18 hours each day. 



Most kinds of farm seeds may, however, be tested in 



