38 



A TEXTBOOK OP BOTANY 



[Ch. in, 5 



powers. Its chemical composition, however, is more il- 

 luminating, for research has shown that protoplasm is not 

 a single substance, but a mixture of many, numbering dozens 

 in even the simplest known organisms 

 (Fig. 14). These substances are vari- 

 ous in complexity, from the simplest 

 inorganic salts, through the sugars 

 and other carbohydrates, to the dis- 

 tinctive proteins, which include the 

 most highly elaborate and unstable of 

 natural chemical compounds. The 

 proteins, indeed, seem to represent the 

 essential basis of the protoplasm, the 

 other substances being more or less 

 secondary or incidental. These many 

 sul)stances, some of which would react 

 with one another, obviously cannot 

 exist heterogeneously intermingled 

 within the same solvent, but must 

 occur in some definite organization. 

 Herein, probably, is to be found the 

 significance of the emulsion or alveolar structure of proto- 

 plasm, wherein the different substances are kept apart in 

 their own separate globular compartments by the neutral 

 continuous substance, which permits, however, upon occa- 

 sion, those regulated interminglings and reactions upon 

 which depend the vital phenomena. At least it seems very 

 clear that most of the physiological powers of protoplasm rest 

 far more upon a chemical than a physical basis. 



This consideration of the chemical constitution of proto- 

 plasm inevitably raises the question, — is there among its 

 chemical substances some one which is the distinctive living 

 substance and to which all the others are subordinate, or 

 do the vital powers inhere in the organization of the mixture, 

 no one constituent being itself alive? We do not yet know. 

 Both views have their advocates. The former fits best w 



Fig. 13. — Protoplasm 

 from the hair cell of 

 a Malva, showing with 

 unusual clearness the 

 alveolar structure ; very 

 highly magnified. (Re- 

 drawn from Biitschli, 

 Microscopic Foams and 

 Protoplasm.) 



I 



