THE SHRINKING AND SWELLING SEED 205 



Measurements in Millimetres of Leguminous Seeds in 

 the three conditions 



Taking the case of the disc-shaped seed of Entada scandens^ 

 we find that the embryo or kernel of the seed swollen for 

 germination is no longer enclosed, as in the pre-resting seed, 

 in soft, yielding coverings, in which it lies easily, filling the 

 space without tension. It is now invested by tough, unyield- 

 ing, drier coverings ; and, whilst the kernel has increased its 

 weight by about 28 per cent, through water-absorption, the 

 coverings are drawn tighter round it than in the pre-resting 

 state. As shown in the regime before illustrated, the kernel 

 that weighed 540 grains in the pre-resting state now weighs 

 690 grains, and the seed, as we have just seen, is rather smaller. 

 The strain produced by the swelling embryo within its 

 tightened coats must be great, and the coverings yield opposite 

 the hilum, the process being purely physical and not necessarily 

 followed by germination, itself a purely biological process in 

 which the active growth of the hypocotyl is involved. The 

 tension within the seed is well illustrated at times when the 

 rupture of the coats is from some cause delayed and one or 

 both of the thick cotyledons within break right across. The 

 selection of the hilum or scar for the seat of the first rupture 

 of the coats is on physical grounds not easy to explain, since 

 the coverings are here thicker than elsewhere ; but this is a 

 point that is discussed in Note 23 of the Appendix. 



The great tension existing within the seed on the eve of 

 germination is also well exemplified in the regimes of the 

 three other leguminous seeds, for which measurements have 

 above been given, viz. Casalpinia sepiaria^ Canavalia obtusifolia^ 



The condi- 

 tions of 

 strain within 

 the swelling 

 seed. 



