19201 AGRICULTURAL BOTANY. 429 



merits thus obtained have been paralleled with irreasurements of the unsatis- 

 fied hydration capacity of living cell nitisses and of dehydrated tissues. The 

 acids and salts have been employed in concentrations mainly within the range 

 of biological possibilities ; that is, in cells in which complete or nearly complete 

 dissociation has taken place. • 



The use of simple methods has served to reveal the general hydration rela- 

 tions of plant protoplasm and the inlluence of acidity and temperature upon 

 growth and swelling; also to uncover the special effects of amido compounds 

 upon hydration and their suggested possibilities in affecting growth. It is 

 noted, however, that the exigencies of life may include conditions under which 

 dehydration of the plasnnitic colloids may reach such a degree that the nature 

 of some of the sugars in growing celLs may be affected. Ore of such changes 

 is the conversion of polysaccharids with a low hydration coelHcient to pentosans 

 with a high liydration capacity, with the resulting succulency or xerophily of 

 the tissue in which this occurs. An aci-nunt in considerable detail is given 

 of the work and its results. 



The delicate balance between water loss and absorption as revealed by 

 measurements of growing organs of all kinds is very striking. The rate at 

 which water is received is generally so little in excess of the transpii-ation 

 that a rise of 10 to 15° C. may extinguish the balance. At the same time such 

 rise of temperature may also result in a lessened hydration capacity, so that 

 by the action of the acids at the higher temperature water may be forced out 

 of the colloidal complex. 



It is considered evident that growth consists of two fundamental features — 

 hydration of the colloidal material of the plasma, and the arrangement of 

 additional material in colloidal structures with the entailed additional capacity 

 for adsorbing water. 



Hydration consists, in the first instance, of the union of molecules of water 

 with the molecules of solid material in the colloidal masses, and it is this 

 action which is entailed in the initial and almost instantaneous enlargement 

 of dried sections when water is poured upon them. The manner in which hydra- 

 tion ensues, or rather the character of its process, will naturally depend upon 

 the character of the cell colloids. Effects which are described are modified or 

 reversed in colloidal material which consists more largely of carbohydrate 

 material. The solubility of protoplasm will depend upon the presence of sub- 

 stances which are indicated. 



The ideal capacity for hydration and growth of any mass of protoplasm 

 would be a resultant of the composition and proportions of its organic material 

 and of the relation of the phases in which they occur. The theoretical maxi- 

 mum of a carbohydrate-protein system is invariably modified by the nutrient 

 salts adsorbed in its structure and by the products of unceasing metabolic 

 changes, especially the transformations which carry compounds through a 

 stage in which acids are formed. These features, as influenced by temperature, 

 determine the rate, daily course, and total expansion in growth. In addition, a 

 certain amount of material is lost in the form of carbon dioxid, and the surface 

 loss of water may on occasion be greater than the amount passing into the 

 growing cell masses. The above-nientioned processes and agencies affect the 

 rate, course, and amount of growth. 



The components and colloidal behavior of protoplasm, D. T. IMac- 

 DouGAL and H. A. Spoehr (Abs. in Science, n. ser., 51 {1920), No. 1328, pp. 595, 

 596). — The authors give summarized accounts of their investigations on 

 biocolloid.s, some of their previous conclusions having been noted (E. S. K., 40, 

 p. 28 ; 41, p. 221 ; and 42, p. 433). 



