DEPARTMENT OF BOTANICAL RESEARCH. 57 



occur theoretically throughout the entire mass of the cell, but in actu- 

 ality would be modified and controlled at every point by the factors 

 which affect hydration. Aggregation of material in syneretic cavities 

 may be taken to present possibilities of the formation of specialized 

 protoplasmic masses or cell-organs or of secretions. 



Many mistaken attempts have been made to bring the growth of 

 organisms and the formation of crystals into the same series of phe- 

 nomena and to establish their identity or continuity. The results 

 of such efforts serve to bemuse the mystic, to divert the philosopher, 

 and to furnish poetical conceptions to wTiters who view matter and 

 all material conceptions from a remote distance. The properties 

 of compounds in crj^stalline form and of matter in a colloidal condi- 

 tion are so •v\dde apart that no serious purpose is accompHshed by 

 the extension of terms to apply to the physical reactions of the two. 



The Growth Mechanism of Protoplasm, hy D. T. MacDougal. 



Adequate experimental studies organized on the basis of data 

 obtained by nimierous analyses have established the fact that proto- 

 plasm of plants consists of a comparatively inert base of pentosans, 

 which may be diffused or transformed only at a very slow rate, in 

 colloidal combination with proteins, amino-acids, lipins, and salts to 

 form a complex mass varying from the liquid condition to that of an 

 elastic gel. The volume and changes in volume constituting growth 

 will be determined by the proportion of water which may be taken 

 up, and this is a resultant of the proportions of the main constituents. 

 Other soluble carbohydrates, including the hexoses, occur in the cell, 

 but not in such concentrations as to affect the enlargement of the proto- 

 plasmic mass directly, but in the vacuoles they may exert an osmotic 

 effect additive to that of the amino-acids which may accumulate in 

 these cavities. 



It is to the osmotic activity of these substances in the vacuoles 

 that turgidity is due, and an important part in the maintenance of the 

 rigidity of organs and other features is to be ascribed to these turgor 

 stresses and tensions. The inadequacy of osmotic phenomena and 

 of the conception of the semi-permeable membrane to provide a mech- 

 anism for the translocation of complex material from cell to cell 

 and the incorporation of new material in a growing mass has long been 

 recognized. That osmotic pressure, however, may play an important 

 part in the enlargement of the plant-cell may well be concluded from 

 the fact that in the stage following the initial sweUing of the embry- 

 onic cell a large share of the increase in volume is due to the increase of 

 the vacuole. It would be a mistake to conclude that the vacuole is 

 a sac charged with electrolytes only, as these ca\'ities invariably hold 

 proteins and carbohydrates in a colloidal condition in which the degree 



