IV Preface. 



rates of metabolism, respiration, hydration, and diffusion may coincide 

 in such manner as to make possible the application of a simple formula 

 for the effects within a range of 15° or 16° C. The relation of growth 

 to temperature for any plant between 10° and 50° C. is not to be 

 expressed by any simple formula. The same general statement may 

 be made concerning light and other agencies, none of which has received 

 more than a fraction of the amount of attention which has been paid 

 to temperature effects. 



The assumption as to the general identity of protoplasm in plants 

 and animals, or even in plants as a group, is one which operates to stifle 

 analytical investigations in a subject of this kind. The relative 

 amounts of proteins, carbohydrates, lipins, and salts in the two groups 

 differ widely. In addition to the capacity of the plant to synthesize 

 carbohydrates, amino-acids, etc., which the animal can not, the res- 

 piration and metabolism of the plant are predominantly carbohydrate, 

 while those of the animal are proteinaceous to a much larger extent. 

 It would seem obvious that a protoplasm rich in fats, high in proteins, 

 and permeated with their derivatives would display an imbibition and 

 growth different from Uving matter in which the base is chiefly the 

 comparatively physiologically inert pentosan groups and which neces- 

 sarily adsorb the salts and acids in a characteristic manner. The 

 unities or general properties of the protoplasm of widely different 

 organisms do not rest upon the presence or proportion of elements or 

 compounds so much as upon the manner in which the necessary con- 

 stituents are brought together. This indispensable condition of life 

 is the colloidal state, in which the substances of living matter form a 

 semi-soUd or elastic gel consisting of over 90 parts water. The mole- 

 cules are large, slow-moving, and adhere to form aggregates as con- 

 trasted with the separation of molecules in the water of solutions. This 

 colloidal structure may be profitably likened to that of a house or fac- ' 

 tory, serving simply as the scene of metabolic processes which take 

 place under special conditions of surface tension. The colloidal labora- 

 tory may be in the form of an emulsion, a reticulum, a sponge, a crystal- 

 line or lamellar structure, with corresponding effects on metabohsm, 

 while the products of respiration may in turn cause alterations in the 

 chambers in which it takes place. ^ 



The purpose of the present work has been to study growth upon the 

 basis of a more inclusive conception than that usually implied in 

 osmosis. The total absorbing capacity of a cell or mass of protoplasm 

 for water is regarded as being exercised in the process of hydration. 

 The som-ce of energy in growth and swelling is the unsatisfied attrac- 

 tion of molecules, or particles or ions bearing an electrical charge. 

 Substances made up in this manner may unite with definite propor- 

 tions of water which becomes part of a symmetrical chemical structure, 

 the union being known in classical chemistry as hydration. In addi- 

 tion, however, it is known that such particles may also adsorb and hold 

 in combination additional molecules of water, an action especially 



