140 PHYSIOLOGY OF NUTRITION. 



determine its weight from time to time (say every half-hour), we 

 shall find that at first a large quantity of water evaporates, and 

 then gradually less and less in each period. 



A few skinned peas are placed in water at about 5 C. Others, 

 as nearly as possible of the same weight, are laid in water at 

 about 20 C. At the end of four hours the seeds are dried and 

 again weighed. It appears that the seeds have taken up more 

 water at the higher than at the lower temperature ; elevation 

 of temperature accelerates therefore the process of imbibition. 

 Some skinned peas are placed in water, and an equal quantity in 

 10 or 20 p.c. solution of common salt. It is easily ascertained by 

 weighing, at the end of a few hours, that imbibition does not 

 proceed so rapidly in salt-solutions as in pure water. 



To investigate the increase of volume experienced in imbibition 

 by seeds, or cubes of wood from different plants, we first place the 

 material in the dry state in a narrow glass cylinder, the volume 

 of which, up to the level of a mark made near the top, is accu- 

 rately known. We now run diluted alcohol into the cylinder 

 from a burette till it reaches the mark, and knowing the volume 

 of alcohol required, we can at once calculate the volume of 

 material used. In determining the volume of the soaked seeds 

 or cubes of wood, we proceed in the same manner, but use water 

 instead of alcohol. By comparative investigations as to the in- 

 crease in weight and volume which plant structures experience 

 in imbibition, we shall often be able to prove, especially in experi- 

 ments with woods, that the actual increase in volume observed 

 by no means corresponds with the volume of water absorbed. 

 This fact is, moreover, quite intelligible if we bear in mind that 

 only the water imbibed by the solid wood substance causes in- 

 crease in volume ; the mere filling of the lumina of the wood 

 elements with water cannot bring about any increase in the 

 volume of the material. Experiments in which we determine at 

 the same time the increase in weight and volume of one and the 

 same piece of wood during absorption are especially instructive, 

 inasmuch as they prove beyond doubt that imbibition is by no 

 means comparable with capillarity. When fluids enter a body 

 by capillary attraction, they always penetrate into previously 

 existing spaces, and therefore capillarity does not give rise to any 

 increase in volume in the fluid-absorbing bodies. When imbibition 

 takes place, the molecules of fluid penetrate between the micellae 

 of the bodies ; they actually make space for themselves between 



