184 



STUDIES IN SEEDS AND FRUITS 



The hydra- 

 tation of per- 

 meable and 

 impermeable 

 resting 

 seeds. 



The resting 

 seed has no 

 use for its 

 water- 

 contents. 



normally in the seed, the life of the air-dried tissues may be 

 re-kindled, but as air-dried substances they have no life in 

 them. 



Another subject upon which the data of the table throw 

 light is the contrast in the hydratation of resting seeds of the 

 permeable and impermeable types. There are four typical 

 seeds of each kind there referred to, and we see that in 

 whatever way we state the relation of the water of hygro- 

 scopicity this contrast is brought out, its proportion in the 

 impermeable seeds being only about two-thirds of that in the 

 permeable seeds. The difference as re-stated below is not 

 very great, but it serves to illustrate the contrast drawn 

 between these two seed-types from a different point of view 

 in the earlier chapters. We now see that the ultra-dryness 

 of impermeable seeds is due to the diminution of the water 

 of hygroscopicity. 



A. In permeable seeds, typified by those of Faba vulgaris, 

 Phaseolus multiflorus y Canavalia ensiformis^ and Alsculus Hippoca- 

 stanum, the water of hygroscopicity forms on the average about 

 6 per cent, of the weight of the moist, living, uncontracted 

 seed, and about 14 per cent, of the weight of the seed in the 

 resting state. 



B. In impermeable seeds, illustrated by those of Guilandina 

 bonducella, Entada scandens, Mucuna urens, and Dioclea reflexa^ its 

 average proportion for the moist, uncontracted seed is about 

 4 per cent., and for the resting seed about 9 per cent. 



And now, in conclusion, let me say that though this treat- 

 ment of the subject, imperfect as it is in many ways, helps 

 to clear the problem of the resting seed, its lifeless, inert 

 condition remains as mysterious as ever. A seed that only 

 holds the water that it would possess whether or not it 

 retains the power of germination can owe nothing to this 

 constituent. Take, for instance, the permeable resting seed 

 with its water -contents ever varying in response to the 

 hygrometric changes of the air. It holds more water in a 

 moist climate than it does in a dry one, and as the experiments 



