CHAPTER IV 



CONDITIONS AND PRINCIPLES OF AB- 

 SORPTION 



THE physical and chemical factors governing the ab- 

 sorption of water and of solutions have long been the ob- 

 ject of careful study. Many phases of such work have 

 been developed in connection with plant physiology. The 

 main facts, however, belong, in large part, to physics and 

 physical chemistry ; yet an appreciation of the essential 

 principles is necessary to an adequate understanding of 

 the mechanism and work of absorbing organs. 



39. Imbibition phenomena. - - Organic bodies of the 

 most varied nature are able to take up water. Commonly, 

 where this water is held within the body by capillarity or 

 surface tension, and where there is produced also more or 

 less swelling, the combined phenomenon is recognized as 

 imbibition in a physiological sense. The hardest wood 

 may absorb water by imbibition, and the force exerted in 

 swelling or warping is capable of lifting or sustaining 

 heavy weights; - - sometimes made use of in splitting solid 

 rock or stone. Dry seed-coats generally exhibit a high 

 degree of imbibition, although these may be infiltrated 

 with substances preventing the absorption of water, and 

 in that way germination may be delayed. 



In the living plant imbibition phenomena are of im- 



G4 



