468 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



to dissolve the whole of the asparagin, only a portion is available for solvent 

 purposes, owing to the localized distribution of the latter. No precipitate could be 

 detected in sections kept at $ C. for a long time, even when the concentration 

 of the cell-sap was more than doubled by plasmolysis. Other amides remained 

 dissolved under similar circumstances, and the data given by Belzung suffice to 

 show that the precipitation observed by him took place in dead cells l . 



Historical. Before Pfeffer, in 1872, showed that proteids may undergo very 

 thorough disintegration in metabolism, the opinion was generally held that the 

 plant avoided as far as possible any dissimilation of proteids when once formed 2 . 

 Th. Hartig had indeed shown that crystalline nitrogenous compounds resulted 

 from proteid decomposition, but his statements were inaccurate on several points, 

 and the remarkable theoretical conclusions which he based upon his observations 

 caused the latter to be disregarded 3 . Since 1876, Schulze, Borodin, c. have 

 brought forward more and more examples of the self-decomposition of proteids, 

 so that the idea becomes more firmly established that an unceasing decomposition 

 of proteids is associated with the continual liberation of kinetic energy necessary 

 in every active protoplast", but it is still doubtful whether such decomposition 

 never ceases in an active cell under any circumstances, even though adult. 

 Detmer ' supposes that this proteid-decomposition is associated with a destruction 

 of the physiological units (Sects. 7 and 8), that is, he postulates a theoretical mode 

 of operation for a process of which neither the universal occurrence nor the actual 

 character have as yet been established. 



SECTION 82. Carbohydrates and Fats.' 



All organic substances are derived from photosynthetic assimilation, 

 and hence the carbohydrates thus produced are the commonest and most 

 abundant organic food-materials. There is a greater production of carbo- 

 hydrate than of any other substance, and every autotrophic plant consumes 

 a large proportion of its synthesized carbohydrates in order to obtain a 

 supply of energy and to produce directly or indirectly its different metabolic 

 products, including all organic reserve food-materials. Carbohydrates and 

 fats form the chief non-nitrogenous substances used for storage, other 

 substances, such as organic acids, &c., being usually present in small 

 amount and only rarely predominating. It is during the early stages of 



1 Cf. Pfeffer, Pflanzenphysiol., I. Aufl., Bd. I, p. 316, footnote ; Oxydationsvorgange in lebenden 

 Zellen, 1889, p. 457 ; Belzung, Ann. d. sci. nat, 1892, vii. ser., T. xv, p. 256. On the insufficiency 

 of Belzung's method, cf. E. Schulze, Zeitschr. f. physiol. Chemie, 1894, Bd. xx, p. 323. 



2 See Ad. Mayer, Agr.-Chem., 1871, i. Aufl., Bd. I, p. 214 ; Pfeffer, Jahrb. f. wiss. Bot., 1872, 

 Bd. vin, p. 530, svhere the older literature is given; Monatsb. d. Berl. Akad., 1873, p. 780. 



1 Th. Hartig, Entwickelungsgesch. d. Pflanzenkeimes, 1858, p. 126. 



* Pfeffer, Landw. Jahrb., 1878, Bd. vn, p. 807. Cf. also E. Schulze, Landw. Jahrb., 1880, 

 Bd. ix, p. 33. 



5 Detmer, Jahrb. f. wiss. Hot., 1879-81, Bd. XII, p. 236; Ber. d. Bot. Ges., 1892, p. 437. 



