THE THREE CONDITIONS OF THE SEED 55 



they are detached in the soft pre-resting state from the green pod, and 

 allowed to go through the shrinking process removed from the parent, 

 brings us face to face with the significance of the impermeability of 

 seeds. A great deal lies behind the fact that under such conditions 

 with a permeable seed the shrinking is too great and the subsequent 

 swelling for germination excessive, whilst with an impermeable seed 

 the shrinking may be deficient and the swelling ratio much reduced 



(P- 47)- 



(21) Illustrations of the behaviour of impermeable seeds in this respect 



are afforded by those of Guilandina bonducella and Dioclea reflexa^ where 

 deficient shrinkage of the large, moist pre-resting seeds leads to a 

 corresponding decrease in the normal swelling capacity and to the loss 

 of impermeability ; and by those of Entada polystachya^ which displays 

 in its two types of normal seeds, permeable and impermeable, a small 

 shrinking capacity and a small swelling ratio for the first, and a large 

 shrinking capacity and a large swelling ratio for the second (pp. 4751). 



(22) Experiments on seeds of the impermeable type in their soft pre- 

 resting condition therefore indicate that a diminution of the shrinkage 

 prevents the acquirement of impermeability and at the same time 

 lessens the amount of water required for germination. This strange 

 relation between the amount of water a seed absorbs in preparing for 

 germination and the permeability or impermeability of the seed- 

 coverings renders necessary an investigation of the distinctive characters 

 associated with these two types of seeds. The question of permeability 

 and impermeability, therefore, blocks the way (p. 52). 



