THE SEED 8 1 



accelerated in narrow capillary vessels ; with an increase 

 of temperature, too, diastase acts more rapidly upon 

 starch. But, we might ask, if physical and chemical 

 processes are accelerated by a rise in temperature why 

 is it that a further rise in temperature depresses the vital 

 activity of the seed ? Why is it that an intermediate, 

 most favourable temperature exists at all ? Is this 

 really a peculiarity of the living organism ? In the 

 meantime no such supposition is necessary. We know 

 that if heat furthers some chemical processes, which 

 contribute to the acceleration of vital processes, it also 

 brings about other effects with which life is incompatible. 

 Albuminoids, for instance, such as enter into the com- 

 position of protoplasm, the foundation of every living cell, 

 coagulate like the white of an egg at about 144 F., 

 and probably begin to change even before that tem- 

 perature. Obviously, if a rise in temperature causes at 

 the same time processes both favourable and unfavour- 

 able to the activity of the seed, that activity will be 

 most energetic at a certain mean temperature when the 

 salutary and the noxious effects of temperature present 

 the most advantageous combination. Thus we see 

 nothing in the effects of temperature on the germinat- 

 ing seed that would induce us to give up the physico- 

 chemical explanation of phenomena taking place under 

 its influence. 



There is one more aspect of the life of seeds, an aspect 

 as yet unfortunately far from being explained, and that 

 is the difference of degree to which different seeds 

 preserve their vitality, i.e. their power to germinate. 

 Some seeds preserve it for years, or even centuries. 

 Others can germinate only within a few days after being 

 separated from the parent plant, and then lose the 

 capacity very quickly ; such are, for instance, coffee 

 beans and willow seeds. Others, again, can germinate 

 only after a considerable lapse of time. In this last 

 group we find most of the stone fruits. Here also closer 



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