392 FOE AGE PLANTS AND THEIR CULTURE 



which is yellow or violet, or both combined. Old seeds 

 become dull and brownish. 



The seed may be adulterated with yellow trefoil ; 

 with old red clover seeds sometimes oiled and polished; 

 and with small or shriveled seed obtained in screenings. 

 Where cheaper foreign clover seed has been added to 

 American seed it may be detected by the presence of cer- 

 tain weed seeds. A 

 3 large proportion of 



small seeds indicates 

 that these have been 

 added. 



The most objection- 

 able weed seeds that 

 may occur in red clover 

 are dodder, Canada 

 thistle, curled dock, 

 buckhorn and oxeye- 

 daisy. 



The best commercial 

 red clover seed may 

 attain a purity of 99 

 per cent and a viability 



of 98 per cent. Good seeds germinate in from 2 to 6 

 days, excepting the " hard " seeds. The percentage of 

 hard see.ds is often 20 per cent and may reach 50 per 

 cent in very fresh seeds. 



The seed varies in weight from 60 to 63 pounds a 

 bushel. One pound contains 279,000 seeds (Stebler), 

 232,000 seeds (Hunter), 200,000 to 240,000 seeds (Hunt). 

 The optimum temperature for germination was found 

 by the Ontario Agricultural College to be 90 Fahrenheit, 

 At 95 the vitality was distinctly impaired. 



FIG. 43. Seeds of red clover. 1, side 

 view and, 2, edge view of seeds ; 3, the 

 triangular form indicatod ; 4, a seed cut 

 lengthwise ; 5, a seed cut crosswise, show- 

 ing the embryo ; a, a seed scar ; b, a 

 stemlet (radicle) of the embryo ; c, seed 

 leaves (cotyledons) of the embryo ; 6, a 

 pod of red clover; 7, natural size of 

 seeds. 



