318 BOTANICAL GAZETTE - [october 



part in the delay. The effect must be attributed to one or both of 

 the inner layers. 



3. As the intact fruit lies in water in the saturated condition, 

 the embryo itself does not half (probably not more than one-fourth 

 or one-fifth) consummate its possible imbibitional and osmotic 

 swelling. The embryo only partly swollen thus lies for years in 

 water, restrained in its swelling by the seed coat, against which it 

 must be exerting a pressure of approximately 100 atmospheres. 



4. The air-dry seed (freed from the carpel wall) when placed in 

 water swells rapidly. It increases 40 per cent of its air-dry weight 

 in the course of two hours. From this time on it shows a slow 

 increase to 50 per cent of its air-dry weight, which is maintained 

 constant even after long periods of soaking. A large part of the 

 water absorption is due to the hydrophilous pectic and hemi- 

 cellulose substances of the seed coat, especially the inner acellular 

 layer. 



5. When the coat cap is removed from the large end of the 

 embryo, thus leaving the embryo more free to continue its imbibi- 

 tional and osmotic swelling, the seed swells even much more rapidly, 

 reaching about 60 per cent of its air-dry weight in two hours and 

 more than 100 per cent after 20 hours. The imbibitional and 

 osmotic swelling gradually passes into growth enlargement. 



6. With the coat cap removed from both ends of the embryo 

 and the seed placed in water, the embryo elongates 19 per cent of 

 its air-dry length in 2.5 hours. This would extend the embryo 

 at least 20 per cent the length of the swollen seed beyond the 



limits of the seed rna/U This elnn oration is all 



imbibitional 



osmotic, involving no growth. Five hours' soaking gives an 



em 



This • 



is only in very small part due to growth. Sixteen hours' soaking 

 gives 36 per cent elongation, which involves considerable growth. 

 Imbibitional and osmotic swelling alone would extend the embryo 



limits 



comDosed almost 



which are very easily transformed by weak acids and bases. Be- 

 sides bringing about chemical changes in these substances, acids 

 and bases change their water relations as is true of hydrophilous 

 colloids in general. 



