THE THREE CONDITIONS OF THE SEED 39 



let us say below 20 per cent, of the weight of the resting seed, 

 that such seeds are on the borderland of vivipary, where they 

 dispense with shrinking and swelling altogether. This con- 

 sideration links itself with some curious reflections that are 

 dealt with subsequently. It is possible that we may have here 

 an explanation of the very low swelling capacity ascribed by 

 Hoffmann to a species of Raphanus (Oetrettig), viz. 8 per cent., 

 which is equivalent to a swelling ratio of i'o8. 



However, the ground will have to be cleared in many The causes 

 directions before we can expect to discover the significance of variation^ 

 such contrasts in the swelling capacities as presented in the tables. the Celling 

 A tentative use of the method of exclusion may perhaps assist 

 us in getting into the right road ; and we will now endeavour 

 to ascertain if there is any connection between these contrasts 

 and certain conspicuous differences in the seeds. In the first 



place, there is the distinction in size. This can be at once dis- (a) Distinc- 



, 1 . .... , , . . tions in size 



missed, since the ordinary variation in the swelling capacity and weight. 



becomes almost a negligible quantity when we reflect on the 

 great differences in size and weight between seeds. Thus the 

 difference in weight between a seed of Primula verts (y^th of a 

 grain) and a seed of Entada scandens (400 grains) is as between 

 i and 40,000 ; yet the difference in their swelling ratios would 

 only be as between 2-3 and 2-5. 



Then, again, it is possible that the distinction between 

 albuminous and exalbuminous seeds may supply a clue to the 

 variation in swelling. Exalbuminous seeds are most character- 

 istic of the Leguminosae ; but plants of the same family with 

 albuminous seeds are fairly represented in the tables. The (6) Albumin- 

 albuminous leguminous seeds there included have the embryo albuminous 

 more or less fully developed, the large, flat cotyledons being seeds - 

 nearly as long and as broad as the kernel. We are therefore 

 employing seeds where the resting period has been imposed at 

 much the same stage of development of the embryo. It will 

 be seen from the comparison made below that such differences 

 do not explain the great variation in the swelling capacity dis- 

 played by seeds of leguminous plants. 



