VITALITY AND VIGOR OF SEEDS 69 



In preventing the absorption of water and oxygen, which are 

 the elements upon which germination in most cases depends, the 

 seed coat and other protective structures are important factors. 



Seed coats that prevent the escape of water and thus protect 

 the embryo against excessive drying also prevent the entrance of 

 water, and, if the seed coat is too impervious to water and air, 

 the germination of the seed is delayed. Seeds which have very 

 hard coats, unless they are treated artificially, must be exposed 

 to the weather until the seed coat is decayed sufficiently to allow 

 the entrance of water and air to the embryo before germination 

 can take place. In a sample of Red Clover, Sweet Clover, and 

 Alfalfa seed, often there are many seeds, known as hard seeds, with 

 coats so hard that germination is delayed or prevented. When 

 sown, they either lie in the ground too long before germination or 

 do not germinate at all. By scratching or pricking their seed coats, 

 so that water and air can enter more readily, they germinate more 

 promptly. Experiments ^ have shown that Clover seed which 

 has been thrashed through a huUer where it is scratched by the 

 spikes germinates much better than seed hulled by hand. This 

 principle is so well recognized that machines especially devised 

 for scratching or pricking the coats of Clover seed have been in- 

 vented. The opening of the seed coats of the Sweet Pea and 

 Canna with a file and Peach pits with a hammer are other in- 

 stances in which the rest period is broken by artificial means. 



In some cases, as in the Hawthorne, delayed germination de- 

 pends upon the embryo, which must undergo a process known as 

 " after-ripening " in which acids, enzymes, or other essential sub- 

 stances are formed. In some weed seeds, delayed germination 

 has been found to depend upon the toughness of the seed coat, 

 which allows water and air to enter, but is so resistant to pressure 

 that it will not allow the embryo to expand until its resistance is 

 weakened by decay. 



Vitality and Vigor of Seeds. — Seeds are worthless for planting 

 imless they have Ufe, or vitality. Not only the vitahty, but also 

 the amount of life or vigor the seed has is an important feature. 

 If the embryo of a seed is dead, the seed will not germinate. If 

 the embryo is lacking in energy, though it may germinate, the 

 plant which it produces will be weak. Only seeds with vigorous 

 embryos are fit for planting. 



' See, Bulletin 177, Vermont Agricultural Experiment Station. 



