104 COMPENDIUM OF GENERAL BOTANY. 



there is a retrogressive movement of water -molecules induced bj 

 this disturbance which continues to the root and which tends to 

 re-establish the "state of saturation." 



Critics rightly observe that the great force with which the 

 water obtained by imbibition is held by the molecules of the cell- 

 wall requires a correspondingly great force to separate it from the 

 molecules of the cell-wall and to guide it onward ; in other words, 

 the force of friction must be very great. From Schwendener's' 

 explanations it is implied that the movement of water in an imbib- 

 ing system is subject to the same law as the movement of water in 

 a capillary system ; that therefore the moving force becomes very 

 great as the diameter of the tubes becomes immeasurably small. 

 Schwendener also discusses the differences between capillarity and 

 imbibition as emphasized by Sachs. From this discussion we select 

 the following : Entrance of water into a solid body in the state of 

 aggregation may take ]>lace whether the volume of the body re- 

 mains the same or whether it becomes smaller or larger ; in this 

 respect capillarity and imbibition are alike. If we suppose a series 

 of glass plates to be superimposed upon each other, the height of 

 this pillar may be increased if the edges are brought in contact 

 with water, provided the spaces between the plates are not too 

 great. If the intervening spaces are increased above a certain 

 limit, the height of the pillar is reduced by capillary action. 

 Therefore we cannot correctly say that when the spaces of a 

 body into which water enters are pre-formed, and when the limit- 

 ing walls of these spaces are firm and immoval)le, friction is great ; 

 and if such spaces are not previously formed, but are produced by 

 the water itself, whereby the volume is increased, friction is re- 

 duced to a mimimum or zero. There is nothing characteristic of 

 capillarity in the immol)ility of the walls of a system, therefore 

 nothing essentially different from imbibition accompanied with in- 

 crease in volume. The term "imbibition" is, however, not 

 superfluous, or synonymous with capillarity. We say a starch- 

 grain is imbibed when it has become saturated with water (from 

 internal causes due to processes of growth (Correns) ivUhout chang- 

 ing its structure. This condition is strictly different from that of 

 swelling, in which water is also taken up (usually a greater or smaller 



1 Untersuchungen iiber das Saftsteigen: Sitz.-Ber. der Berl. Akad., 1886. 



