ADDITIONAL EVIDENCE 127 



leguminous seeds {Adenanthera pavonina, Entada scandens, 

 Mucuna urens) give an average gain in air of 5*0 per cent., 

 with an average water-percentage of 11 "7. These results may 

 be accepted tentatively as representing the average behaviour of 

 impermeable seeds when broken up and exposed to the air, viz. : 



Seeds holding ii*7 per cent, of water gain 5*0 per cent. 

 5j 7'S » 5> 9'2 jj 



At best this is only a rough indication, as each seed has a 

 regime of its own in this respect. The real significance of 

 these figures becomes more apparent when we contrast them 

 generally with those for permeable seeds of the same order, 

 taking as our examples the seeds of Canavalia ensiformis, Faba 

 vulgaris (Broad Bean), Phaseolus multiflorus (Scarlet-runner), 

 and Pisum sativum (Pea), which hold on the average about 1 5 

 per cent, of water when the drying process is complete, and make 

 no permanent addition to their weight when broken up or cut 

 open or laid bare and exposed to the air. Contrasted with 

 impermeable seeds we get these general results : — 



Impermeable seeds holding 7-5 per cent, of water add 9*2 per cent. 



to their weight. 

 Impermeable seeds holding ii-7 per cent, of water add 5-0 per cent. 



to their weight. 

 Permeable seeds holding 15-0 per cent, of water add O-o, behaving 



hygroscopically. 



Numerous 'disturbing influences come into play in making 

 a rough estimate, such as that given above ; but its general 

 indications are confirmed by the results obtained from experi- 

 ments in which such influences are largely eliminated, namely. The eliraina- 

 by contrasting the seeds of the same plant in those species ^"bingtal 

 where both permeable and impermeable seeds are represented, ^QnJJ.^®gy^y 

 namely, in the variable group. But even here, as indicated seeds of the 

 in the table, we must be able to distinguish between samples wi^re^'both 

 containing very difi^erent proportions of these two kinds of types occur. 

 seeds. -There is a practical difficulty in ascertaining a seed's 



