4 Hydration and Growth. 



a hydrogen-ion concentration above the iso-electric point, or, as com- 

 monly expressed, when in a state of acidosis, in consequence of which 

 many sweeping premature generaUzations have been made as to the 

 relations of electrolytes to protoplasm. Plant protoplasm, in so far as 

 the higher forms are concerned, is poor in lipins, is usually characterized 

 by a major proportion of carbohydrates, although in such simple forms 

 as the bacteria the protein content may be very high. The water- 

 relations of a cell-mass in plants will naturally be determined by its 

 protein-carbohydrate ratio, with the implied corollary that a varying 

 hydration capacity is displayed which may reach its maximum in a 

 condition of acidosis in forms rich in nitrogen, and in a neutralized, 

 relatively salt-free condition in those in which the proportion of col- 

 loidal carbohydrate is relatively great. 



Cytological science recognizes that homogeneous states of the col- 

 loids do not prevail throughout the cell and a vast literature has grown 

 up concerning the masses of unlike composition, structure, and form, 

 some of morphological value, which make' up the cell-body. Attention 

 has naturally been concentrated on the more readily visible, durable, 

 and measurable bodies, some of which are indubitably the scene of per- 

 formances of the first rank, and form the chief mechanism in genetics. 



It is not to be forgotten, however, that the diverse mixtures of gels 

 and sols constituting the greater part of the protoplasmic mass, the 

 structure of which may not be resolved by direct microscopical methods, 

 is the ultimate colloidal machine in which the organs of the cell are 

 built up, torn down, and metamorphosed. The study of some of the 

 sohd bodies in the protoplasm may yield the same comprehension of 

 the play of chemical energy and surface tension of Uving matter as 

 might be gained of the cyclonic forces of a storm by a measurement and 

 dissection of hailstones. The greatest possibilities in cell mechanics are 

 those which lie in the changes in viscosity, volume, and water-relations 

 of cell-organs as determined by the composition and arrangement of 

 the colloidal emulsion or mesh and the nature of the metabolism which 

 goes on in its sols and gels. 



It is also to be emphasized that it is not only untrue but unprofitable 

 to assume that the li\ring matter of plants and animals have the same 

 general chemical properties. The difference in the occurence and r61es 

 of hpin in the two groups is fundamental, and, in addition to the water- 

 relations, the metabolisms of the two present differences not attributable 

 simply to the carbohydrate-protein ratio in their composition. Thus 

 the Uving matter of plants includes within its metabolic cycles such 

 features as the sjmthesis of the carbohydrates and of the amino-acids, 

 the last-named capacity being exhibited only to a very limited extent 

 by animals, which, in the main, are characterized by a metabolism of 

 sugars notably different from that of the plant. 



