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-longevity would seem therefore to be determined by two 

 independent eventualities, the limit of the impermeability of 

 the coats and the limit of the staying power of the protoplasm 

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

 lasts the longest. Amongst the results of Professor Ewart's 

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

 vived 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 sorpe 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 first is : Under which conditions would an imper- 

 meable seed retain its vitality longest, in the air or in the soil } 

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

 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. 



