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 atall. 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 huller 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 
“ sfter-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 
unless they have life, or vitality. Not only the vitality, 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. 
1 See, Bulletin 177, Vermont Agricultural Experiment Station. 
