64 STUDIES IN SEEDS AND FRUITS 



soil for very long periods without losing their impermeability. 

 Under such conditions he found that all Acacia seeds found 

 below the surface possessed impermeable coats and required 

 special treatment to produce swelling and germination. 



Whether or not the seeds always retain their vitality when 



they preserve their impermeability is another matter, since 



longevity, as Professor Ewart observes, may not depend 



primarily on the impermeability of the seed-coats, but on a 



peculiar inherent property of the protoplasm, the duration of 



which under the soil is secured by the impermeable coverings. 



Seed- Seed-longevity would seem therefore to be determined by two 



termined by independent eventualities, the limit of the impermeability of 



the imper f t^e coats and the limit of the staying power of the protoplasm 



meabihty of o f the kernel or embryo ; and the question arises as to which 



the coats and J i r -r* r T-> 



by the limit lasts the longest. Amongst the results or Professor rLwart s 

 ing power of experiments it is easy to find cases where impermeability has sur- 

 the embryo. v i vec j its utility ; but it would be hazardous to assert that this is 

 the usual course of events under the soil. This method of stat- 

 ing the problem seems to be the best way of reconciling the views 

 of Mr Crocker in America and Professor Ewart in Australia. 



An important outcome of these two series of investigations 

 is that the issues can be narrowed, thus permitting one to dis- 

 tinguish between the extrinsic and the intrinsic in the results 

 of experiments. Results applicable to the behaviour of the 

 seed in air are in a sense extrinsic, since such are not the usual 

 conditions under which Nature tests its longevity. Those that 

 can be brought into some kind of relation with the seed as it 

 occurs naturally in the soil are likely to be the most instructive. 

 Two questions, it would seem, have shaped themselves whilst 

 considering these results. 



The two The first is : Under which conditions would an imper- 



raised by the meable seed retain its vitality longest, in the air or in the soil ? 



tionsfof Mr The second is : Which has the greatest staying power, the 



Crocker and impermeability of the seed-coats, or the germinative capacity 



of the kernel ? Notwithstanding the evidence before us, the 



answer to both of them is indeterminate. 



