io6 The Living Plant 



Class I. The BASAL FOOD, or PHOTOSYNTHETIC SUGAR; the substance first 

 formed in lighted green leaves; composition CeH^Oc. 



Class II. The FOODS, active and reserve, and the SKELETON; chemically 

 called CARBOHYDRATES, with a composition identical with or 

 readily transformable from that of the photosynthate, viz., 

 CeHiaOe, or Ci2H 22 Oii, or (C 6 Hio0 5 )n. 



Class III. The SECRETIONS; various non-nitrogenous substances, mostly of 

 special ecological functions, DERIVATIVES OF CARBOHYDRATES 

 and containing the same elements, but in markedly different 

 proportions, and hence collectively expressible only in the form 

 C n H n O n . 



Class IV. The NITROGEN-ASSIMILATES, chemically called AMIDES; inconspic- 

 uous but important substances containing the elements of the 

 photosynthate with the addition of nitrogen, and forming the 

 transition from Class I to Class VI; collectively expressible 

 only as C n H n O n N n . 



Class V. The PRINCIPAL POISONS, chemically called ALKALOIDS; containing 

 (as a rule) the elements of the Amides but in different pro- 

 portions, substances of uncertain meaning, and collectively 

 expressible as C n H n (O n ) N n . 



Class VI. The FLESH-FORMERS, chemically called PROTEINS, contributing 

 to the formation of protoplasm and consisting of the elements 

 of the Amides with the addition of sulphur and phosphorus, 

 and collectively expressible only as C n H n O n N n S n (P n ) 



Class VII. The REGULATORS OF METABOLISM, called ENZYMES, substances 

 of unknown composition, but supposed to be proteins, possess- 

 ing remarkable properties of causing chemical transformations 

 in other substances. 



Class VIII. LIVING PROTOPLASM. 



Class I. The Basal Food, or Photosynthetic Sugar 



This substance needs no introduction to the reader of the earlier 

 parts of this book; but for others it may be characterized as a 

 sugar made abundantly in the lighted green leaves of plants from 

 carbon dioxide and water, and forming the foundation of all 

 organic substances. It belongs in a class by itself only because 

 of its unique mode of formation and function, for chemically 

 it belongs in the second class, being nothing other than a mixture 

 of the grape and fruit sugars next to be described. 



