THE ROLE OF WATER 423 



The tenacity with which tissues hold imbibed (adsorbed) water 

 is illustrated by an example of R. Newton. The succulent stems 

 of a cactus were put in a desiccator (drying chamber) over 

 sulphuric acid. After six months, in an atmosphere of almost 

 zero humidity, the juicy stems had lost but 10 per cent of their 

 water. The stems remained dormant and, on being returned 

 to a moist atmosphere, sprouted. Continuing his studies on 

 this problem with Gortner, Newton found a direct correlation 

 between winter hardiness (resistance to freezing) in wheat 

 and percentage of bound water, the explanation being that as 

 adsorbed water does not freeze, while free water does, the more 

 of its total water supply a plant can hold in the bound state the 

 more able it is to withstand low winter temperatures. W. 

 Robinson carried this field of investigation over into the life of 

 insects and found there the same correlation. The pupae of 

 two hardy species of insects which, in cocoons, are exposed to 

 low winter temperatures, gained in bound water and lost in free 

 water under the stress of falling temperature, while a nonhardy 

 weevil which cannot survive below freezing lost bound water in 

 a falling temperature. Robinson's conclusion for insects is the 

 same as that of Newton and Gortner for plants, viz., that since 

 bound water will not freeze at low temperatures, the greater 

 the quantity of water that can be converted into that form and 

 the more rapidly it can be done the greater is the protection 

 against freezing afforded to that species. 



The foregoing hypotheses are undoubtedly true in part, but 

 resistance to drought and freezing in plants and animals is 

 probably more than a question of relative amounts of free 

 and adsorbed water; other factors enter in, such as the waxy 

 coverings on cacti, which are a great protection against the 

 loss of water. Furthermore, some plants and fruits with much 

 free water, such as tomatoes, resist freezing at fairly low 

 temperatures. 



Newer concepts concerning the hydrogen ion lead to the belief 

 that when water reacts with an acid, H3O+ + Cl~ are formed 

 (page 301). It has been suggested that so-called bound water 

 may be H3O in distinction to H2O. 



In spite of questions and criticisms, the concept of bound water 

 and its biological significance is becoming more and more firmly 

 established. 



