ADDITIONAL EVIDENCE 143 



case of permeable and impermeable seeds. Thus, assuming 

 that the seed gave up approximately all its water when deprived 

 of the protection of its coats, then the permeable seeds entire 

 in their coverings may be regarded as having lost as much as 

 from 70 to 80 per cent, of their water-contents, whilst the im- 

 permeable seeds in the same entire condition and exposed to 

 precisely the same test lost barely 25 per cent. 



Further contrasts in the behaviour of permeable and im- 

 permeable seeds when exposed in their coats to a temperature 

 of 100° to 110° C. for two hours are exhibited when we compare 

 the results of their efforts to regain the lost water from the 

 air. With impermeable seeds we have seen that very little 

 effort is made to gain back their original weight, and that after 

 the oven test they resume their impervious character, doggedly 

 refusing to make any response to the hygrometric changes of 

 the air and adding nothing to their weight when immersed in 

 water. On the other hand, after the oven test permeable seeds 

 slowly regained the water lost, but so very slowly that six weeks 

 in the cases of Faba vulgaris and Phaseolus multiflorus and two 

 weeks in the case of Pisum sativum were occupied in returning 

 to their original weight. The influence of the coats is especially 

 brought out in the case of the two types of seeds, if we regard 

 their behaviour when the seed is broken up and is thus deprived 

 of the protection of its coats. After the oven test the imper- 

 meable seed gains back in a few days all the water lost and a 

 considerable percentage (5 to 10 per cent.) more ; whilst the 

 permeable seed returns to its original weight in a week or two, 

 and is subject then to only the normal hygroscopic variations. 



The differences in the nature of the protection afforded by Summing-up 

 the coats of permeable and impermeable seeds when exposed for ences in the" 

 two hours to a temperature of 100° to 110° C. may be thus behaviour of 

 briefly stated. In the impermeable seed the coats only allow and imper- 

 one-fourth of the water-contents to escape, and by subsequently when ex-^ ^ 

 resuming their imperviousness practically frustrate the seed's coats^to wJh 

 effort to gain back the loss. In the permeable seed the in- tempera- 

 hibitive influence of the coats is so slight that three-fourths of 



