THE NATURE OF SEEDS 



339 



afforded by the testa, the compactness of the tissues within 

 the testa being an additional protection of minor impor- 

 tance. If there are two integuments, it is the outer one 

 which forms the testa. (See page 276.) At maturity 

 the testa is usually hard and bony, being composed of 

 layers of cells with greatly thickened walls. In most one- 

 seeded fruits, as in grains and akenes, the pericarp closely 

 surrounds the seed and, in such cases, it, rather than the 

 testa, affords the chief protection. 



D. Vitality of Seeds. — Some seeds are able to germinate 

 and produce good plants many years after their formation, 

 and after long exposure to conditions which ordinarily put 

 a stop to lif e very quickly. Nothing shows the capacity of 

 seeds to protect the embryos within them so well as their 

 length of lif e and their power to endure conditions unfavor- 

 able to life. 



Some seeds, those of willow for example, die unless they 

 germinate almost immediately, but short-lived seeds are 

 the exception rather than the rule. 



Certain popular stories about the length of lif e of seeds are 

 without foundation. Such, for example, is the story of 

 mummy wheat. It has been widely told and believed that 

 wheat found in the wrappings of ancient Egyptian mummies 

 was successfully sprouted. There is no doubt that the 

 mummies were many hundreds of years old, but there is 

 also no doubt that the wheat was much younger than the 

 mummies. It was put there to fool people. The facts, 

 however, are wonderful enough without exaggerating them. 

 Probably the longest-lived seeds are among those produced 

 by the pea family. There is good evidence that some 

 such seeds may retain their vitality as long as two hundred 



