THE SHRINKING AND SWELLING SEED 215 



absorbing water when preparing for germination, a Ricinus seed 

 adds only one-third to its weight. It is probable that the 

 small swelling ratios of many of the seeds mentioned in the 

 table of the results obtained by Hoffmann and Nobbe in 

 Chapter II. {Brassica, Raphanus, Cannabis, Camelina, Heliafithus, 

 and Pinus) result from the oil in the kernels. 



That oil takes the place of water in the kernel is shown when 

 . we compare the water-percentages of the kernels of permeable 

 resting seeds. In Hura crepitans the water-contents of the 

 kernel amount to 87 per cent. ; in Ricinus they form 6 per 

 cent. ; whilst with the kernels of the four leguminous plants 

 dealt with in the tabulated summary, the water-percentage 

 ranges between 14 and 16. In the cases of certain Palm seeds 

 oil plays a prominent part in determining the regime. The 

 water-percentage is low When the spontaneous drying is 

 complete. Thus in Elteis guineensis it is 9 per cent., and in the 

 Coco-nut about 7 per cent., this small percentage of water 

 being connected with the large amount of oil present. 



It will be appropriate here to make a few remarks on the The decrease 

 decrease in the relative weight of the seed-coats as the seed weight of ^ 

 matures in the ripening fruit. Just as the growth of the coate|s"ti,e 

 pericarp is always in advance of the seed-growth, so the growth seed ripens, 

 of the seed's coverings is always in advance of that of the 

 kernel or seed proper. Thus with Guilandina bonducella the 

 weight of the coats of the full-sized soft seed in the mature 

 moist pod is about 61 per cent, of the total weight of the seed. 

 A little earlier in the history of the seed's growth it is about 

 66 per cent., and earlier still, when the seed is not much over 

 half size and the embryo incompletely formed, it is about 70 

 per cent. The behaviour of the seeds of the Horse-chestnut 

 \MscuIus Hippocastanum) as they ripen in the capsule well 

 illustrate this progressive change. When the seed is only 

 one-fourth grown the coats form 46 per cent, of the weight of 

 the entire seed, when half size 42 per cent., and when full size 

 2,^ per cent. In this connection again let us take the data 

 afforded by Peas {Pisum sativum) from the same set of plants. 



