378 A TEXTBOOK OF BOTANY [Ch. VIII, 3 



to a scarcely perceptible motion. Indeed, so slow are the 

 life processes in ordinary dry seeds that, as tested by the 

 most important and typical process of them all, viz. res- 

 piration, they are not actually demonstrable by even the 

 very refined methods of research which have been applied 

 to the problem. Accordingly some investigators have main- 

 tained that the processes are actually suspended, as an en- 

 gine may be stopped, all ready to start again when suitable 

 conditions are supplied. But the collective evidence, in- 

 direct as well as direct, seems rather to indicate that the 

 processes never stop completely so long as the seed remains 

 capable of germination. 



The extent to which the conditions of life in seeds differ 

 from those of ordinary active life is attested by the extremes 

 of temperature they can endure without injury. Thus well- 

 dried seeds can be kept some time above the boiling point 

 of water (100° C.) without damage, though active embryos 

 would be killed very quickly by an exposure to only 60° C. 

 Again, seeds have been kept for days surrounded by liquid 

 air, at a temperature of — 194° C, and then have germinated 

 freely, though active embryos would perish at 0° C. And 

 seeds can endure some other untoward agencies in like man- 

 ner. It is the same with the thick-walled resting spores of 

 Fungi and Bacteria. 



The resting period, also called delayed germination, 

 of seeds, is less familiar, but equally important. Some seeds 

 of wild plants will germinate as soon as mature, if given 

 favorable conditions of moisture and warmth; most kinds, 

 however, first remain quiescent for days, weeks, months, or 

 even years. Essentially the same phenomenon appears in 

 the buds of trees and shrubs, for if twigs are brought into the 

 warm greenhouse and placed in water, most buds will not 

 start at all before February, though later, under precisely 

 the same treatment, they will open and display their 

 flowers to perfection. Bulbs and tubers (e.g. potatoes) act 

 in a similar manner. It is true that some individual flower 



