388 BOTANICAL GAZETTE [may 



lower rate. Two explanations suggest themselves for this. The coat 

 may absorb water more readily than seed substance, and the initial 

 intake may represent the saturation of the seed coat, or the rapid 

 initial intake may be caused by the fact that at first the absorb- 

 ing substance and water are in direct contact, but after a short time 

 the water absorbed by the interior of the seed must penetrate a 

 layer of saturated substance before it can reach the actively absorb- 

 ing material. This outer saturated layer may offer resistance to 

 intake in the form of friction with the moving water. As this 

 layer becomes thicker and thicker all the time, it may tend more 

 and more to reduce the absorption rate. Changes in the velocity 

 of absorption due to such causes might be found in any case of 

 water intake. 



Finally, something should be said about the rise in the intake 

 rate in split peas after a certain critical percentage of intake has 

 been reached. During absorption one can observe that the hemi- 

 spherical cotyledons become swollen first around the thin edge 

 where water is penetrating from both sides. Looking at the 

 flat side of the cotyledon, one can see that the edge has 

 become raised up, while the center remains as it was origi- 

 nally, and appears depressed. The flat side has become con- 

 cave. It seems evident that a band of dry material extends 

 across the middle of the cotyledon from the center of the spherical 

 side to the center of the flat side, and that imbibition forces at 

 work in the edge of the seed are pulling at this dry band. After 

 the critical intake has been reached, the center of the flat side soon 

 swells out, and the concavity disappears. It is practically certain 

 that the seed substance actually cracks apart during this process, 

 leaving interior cavities that fill up with water. This idea is 

 strongly supported by unpublished data, collected by Dudley J. 

 Pratt, who worked in the laboratory of the University of Kansas, 

 on the effects of acids and bases on the swelling of pea cotyledons. 

 He was able to detect clearly the formation of such cavities during 

 absorption, and some of them are of considerable size, as when 

 strong hydrates or acids cause excessive swelling. This breaking 

 up of the internal tissues of the cotyledon satisfactorily accounts 

 for the peculiarities observed in absorption curves in split peas. 



