350 FORAGE PLANTS AND THEIR CULTURE 



but more than this is certainly an adulteration. To 

 detect trefoil and bur clover seeds, careful examination 

 is necessary. Very commonly both of these are added as 

 adulterants, especially to European seed. Old alfalfa seed, 

 as well as shriveled seed, has a dull reddish brown color. 



Troublesome weeds that may be present in alfalfa are 

 Canada thistle, dodder, curled dock, quack-grass, wild 

 carrot and oxeye-daisy. 



Good commercial seed may attain a purity of 98-99 

 per cent and a viability of 97-99 per cent. A bushel weighs 

 from 60 to 63 pounds. One pound contains 182,000 to 

 237,000 seeds, an average of about 220,000. Usually a 

 small per cent of the seed is hard, especially if the seed is 

 new. Good seeds germinate within 6 days and mostly 

 in 2 or 3 days. 



415. Viability of seed. Alfalfa seed retains its via- 

 bility for many years, depending partly on the conditions 

 of storage. Seed of the season does not germinate as well 

 as that one year old. 4 . 



The best alfalfa seed is characterized by its plumpness 

 and a decidedly yellowish color. Dead seeds become 

 reddish brown and are easily distinguished. Turkestan 

 alfalfa seed is trampled out by animals, and may often be 

 recognized by its dusty appearance and the presence of 

 small pebbles. 



In all alfalfa seed a varying percentage is " hard " ; 

 that is, does not absorb water and germinate promptly. 

 There are no published data regarding the behavior of 

 hard seeds in the soil, but the probability . is that some of 

 them remain dormant a long time and hence are practically 

 worthless. 



At the Colorado Experiment Station samples preserved 

 in envelopes and vials for six years showed a range of ger- 



