Imbibition and Growth in Fruits. 173 



in solubility or dispersibility. One group which may. be illustrated 

 by agar has a definitely limited swelling capacity under temperatures 

 below 50 C. and other conditions, and of course is not soluble. Others, 

 like the mucilages of Opuntia or acacia or tragacanth, are soluble, and 

 when placed in water pass from a dry solid state to a complete solution. 

 The solubility of protoplasm will depend upon the presence of these 

 substances, as well as upon the albumins which may be present. 



The ideal capacity for hydration and growth of any mass of proto- 

 plasm 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 maximum hydration 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 trans- 

 formations which are comprehended in respiration and 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 

 from the plant in the form of carbon dioxid, and, as has been emphasized 

 on the preceding pages, the surface loss of water may on occasion be 

 greater than the amount passing into the growing cell-masses. The 

 above-mentioned processes and agencies affect the rate, course, and 

 amount of growth. 



