134 STUDIES IN SEEDS AND FRUITS 



moist seed loses in the oven that it could never regain. Such 

 considerations render necessary a review of the general behaviour 

 of seeds after exposure to the oven test. It will be shown 

 in the following chapters that the whole problem can be 

 stated in quite a different manner if we introduce the principle 

 of Berthelot as a resolving factor. 

 Explanation The following table is intended to illustrate the contrast 



instable. " between impermeable and permeable seeds in their capacity 

 of increasing their weight by absorbing water from the air 

 when exposed in the broken condition, either with or without 

 a previous exposure to a temperature of ioo° to i io° C. 

 It will be noticed that in impermeable seeds both the coats 

 and kernel possess this quality of adding considerably to their 

 weight when exposed unheated to the air ; whilst with perme- 

 able seeds both coats and kernel retain their weight, merely 

 displaying the normal hygroscopic variation of 2 or 3 per 

 cent., 98*5 to ioi*5. Usually the inability to increase the 

 weight, except in the ordinary course of hygroscopic variation, 

 is indicated by 100. A previous exposure in the oven for 

 i^ or 2 hours does not materially affect the behaviour of 

 the seed or its parts. In the case of impermeable seeds 

 much the same excess weight is attained in about five days 

 after the oven test, whilst in permeable seeds the original 

 weight is more or less regained during the same period after 

 the heating ; and in those cases where there is a marked 

 failure to return to the original weight, it can be shown either 

 that the seed had not completed its drying process before the 

 experiment, or that the period of exposure to the air was too 

 short, a week or two being in their case required (see p. 142). 

 The behaviour of variable seeds is of course intermediate in 

 character. ..." Similar samples " used in certain experi- 

 ments were samples wliere each seed tested had been divided 

 between the two samples, so that truly mixed samples were 

 simultaneously experimented on. The same object was effected 

 in the case of large seeds like those of Entada scandens (weighing 

 some 500 grains) by employing the same seed for both samples. 



