26 POPULAR EEEOKS. 



prolonging the life of a seed. Probably seeds 

 never lose their vitality from having entirely 

 exhausted their supply of stored up food. The fact 

 that seeds may germinate again and again, after 

 having their store diminished by previous attempts 

 at vegetation, shows that for at least the first stages 

 of germination most seeds contain more nutriment 

 than they need. There are two agents nearly 

 everywhere present reducing all organized matter 

 to the inorganic state; that is to say, two causes 

 at work producing decay in everything of an ani- 

 mal or vegetable nature. These causes are, first, 

 the oxygen of the air ; second, numerous low forms 

 of vegetable life which feed upon decaying organic 

 matter and assist in producing decay. These out- 

 side sources of destruction are far more active 

 in their, demands upon the seed than is the living 

 plant which it contains. To protect themselves 

 against these destructive influences seeds are en- 

 closed in a more or less impervious covering; and the 

 length of time during which seeds will live depends 

 very much upon the nature of this covering. The 

 differences in duration of vitality among seeds how- 

 ever depend probably even more on the composi- 

 tion of the seed itself than on the character of its 

 covering. Why it is that the thick- shelled Chestnut, 

 Walnut and Hickory will retain their vitality only 

 a few months, while the thin-skinned grains of corn, 



