LUCERNE OR PURPLE AIEDICK ; ALFALFA 645 



ance to the penetration of water depends on the nature of 

 the 'hard layer' of the testa. Formerly it was supposed 

 that the thickness of this layer and waxy substances within 

 it prevented access of water into the interior of the seed. 

 This, however, is not the case, the defect being due to the 

 great amount of ash-ingredients, especially silica and lime, 

 which it contains. The coat of ' hard seeds ' is capable 

 of resisting acids and boiling water, but even very slight 

 friction — a few scratches with a needle — is sufficient to 

 enable the seed to absorb water readily. In order to im- 

 prove the germination capacity of the hard seeds in samples, 

 the latter are shaken up in a sack with sharp sand. Fric- 

 tion inside cylinders lined with thin layers of cement, in 

 which is embedded sharp sand, is also adopted for the same 

 purpose. 



The number of ' hard seeds ' in a sample is dependent on 

 the nature of the seed to some extent, the wild vetches 

 having usually from 50 to 90 per cent. Season and climate 

 also influence it. 



Lucerne or Purple Medick; Alfalfa {Medicago sativa L.). — 

 True seeds are sown for a crop. 



Form and Size. — The seeds of Lucerne are very irregular 

 in form, some of them being kidney- 

 shaped, and of variable length; 

 others are more or less oval, with 

 an irregular angular outline (see Fig. 

 195). The radicle is more than half 

 the length of the seed, and its posi- 

 tion is generally seen on the outside. 

 The seeds are often wanting in „ „ , , 



" fiG. 195. — two commonest forms of 



plumpness. When placed on edge lucerne seeds. 1 



' All the figures of seeds in this chapter, e.'ccept Fig. 206, are drawn ten 

 times the natural size. 



