CH. VIII, 3] VITALITY OF SEEDS 379 



buds, like some individual seeds, will start in the fall; but 

 such cases are clearly abnormalities or variations, due to 

 failure of the control mechanism to operate (page 342) ; and 

 the result is always fatal. It is thus evident that the resting 

 period is not simply an incident of seed and bud life, but is 

 obligatory, so to speak, under natural conditions, though it 

 can be shortened artificially in a good many cases. The 

 functional value, or necessity, of the resting period is obvious, 

 since it tends to prevent the germination of seeds and open- 

 ing of buds in warm times of late autumn or winter, when sub- 

 sequent freezing must inevitably kill the new growth. As to 

 the physical basis of the resting period (the method by which 

 it is enforced on the seed), that seems to be diverse. In 

 some cases it is known to depend upon the embryo, con- 

 sisting in a slow " after-ripening," i.e. formation of enzymes, 

 acids, or other essential substances; but in other cases it 

 has been proven to depend upon the character of the seed 

 coats, which are so constructed as to prevent the admission 

 of oxygen or of water, both indispensable to germination, 

 the inhibition continuing until the coats are ruptured by de- 

 cay. It is of course a necessary corollary of this explanation 

 that in such cases germination will be prompt if the seed 

 coats are artificially broken ; and such is found by experiment 

 to be true and has long been known to nurserymen and 

 gardeners. Thus, they break Peach pits with a hammer, open 

 Canna seeds with a file, and bruise or break the coats of 

 others in diverse ways, thereby greatly hastening the germi- 

 nation of those kinds. 



While the seeds of most plants have a resting period, 

 cultivated plants seem mostly to lack it. Thus, we grow 

 Corn, Beans, Peas, and other crop plants in our laboratories 

 in autumn from seeds of that summer. This peculiarity, 

 indeed, sometimes brings loss to the farmer, since in excep- 

 tionally warm wet autumns, grain is apt to germinate in the 

 ear in the standing crop, to its very great damage. The 

 resting period has presumably been lost from cultivated 



