Chapter VI — 69 — Intracellular Distribution 



tein molecules; (c) water soluble dyes and salts diffuse freely and rapidly 

 within the cell; and (d) the evidence .... shows that protoplasm without 

 a special surface membrane is freely miscible with water." Chambers 

 (1944) also regards water as the continuous phase in protoplasm, as evi- 

 denced by microinjection experiments. The ready diffusion of aqueous 

 solutions thi'ough cytoplasm, the formation of discrete droplets by water 

 immiscible liquids, the rapid freezing of water in cytoplasm when inocu- 

 lated, all are strong evidence. 



We must therefore at present accept the working hypothesis that water 

 forms a continuous phase in protoplasm. 



It should be obvious from the foregoing discussion that forces of many 

 types are involved in the hydration of protoplasm, and at present it is im- 

 possible to analyse completely the various interrelations of these forces. 

 Keeping in mind the unique nature of the living protoplasm, the intricate 

 and involved processes going on, and the almost insurmountable difficulties 

 presented by the complexity of the energy relations, it seems that a clear 

 picture of protoplasmic function must await years of patient research. 



Water in Vacuoles : — Vacuolar sap may consist of as much as 98 per 

 cent water ; it has the highest water content of the three cellular phases. In 

 it are found a miscellaneous and variable assortment of sugars, salts, acids, 

 pigments, etc. Its composition among different plants is extremely variable. 



The colloid content of vacuolar sap may be appreciable in some species. 

 In conifers, tannins, gums, resins, and other substances have been demon- 

 strated, and some (e.g., Roberts and Styles, 1939) have, correctly we 

 believe, stressed their importance in the water relations of the cell. 



The substances which most commonly comprise the hydrophilic col- 

 loidal fraction of vacuoles, at least in the higher plants, are proteins, tannins, 

 and mucilages. Tannins may be found combined to some degree with pro- 

 teins or mucilages. Other colloidal substances of a fatty nature such as 

 lipids, phosphatides, and phytosterols may be present (cf. Guilliermond, 

 1941, p. 164). 



An especially high vacuolar colloid content in petal cells of certain 

 Boraginaceae can be demonstrated (Gicklhorn and Weber, 1926). Ap- 

 parently the sap may even solidify. The solidification follows a spontaneous 

 contraction of the vacuole, plasmolysis, or vital staining. On treatment 

 with neutral red solutions the sap separates into two phases, an inner gel 

 and, between the gel and the cytoplasm, an optically clear watery solution. 

 Hofmeister (1940a, b), who has recently investigated the problem by 

 micrurgical methods, concludes that the neutral red effect is a precipitation 

 reaction (coacervate formation), while the plasmolytic and vacuolar con- 

 traction phenomena are of the nature of syneresis. 



Microchemical tests by Hofmeister (1940&) on cells of Symphytum 

 officinale showed no tannin, protein, or cellulose in the vacuolar sap. Large 

 quantities of pectin, however, were indicated. Other examples of vacuoles 

 containing sap of a jelly-like consistency are known (Guilliermond, 1941, 

 p. 154). 



The vacuolar sap of most cells has been considered to be essentially a 

 true solution. The researches of Hoagland and Davis (1923, 1929), 

 Collander (1939), Lundegardh (1940), and others indicate the high 

 content of nutrient salts that occur in solution in plant cells. In addition 

 to salts, sugars are of great importance in determining the water retention 

 of cells. On the other hand, one must recognize the complex nature of the 



