464 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



It is possible that the continuance of protcid-decomposition is essential to 

 all organisms, although this cannot be postulated with absolute certainty 

 in the case of adult cells. It may even happen that respiration need not 

 necessarily involve any marked disintegration of proteid material (Sect. 101). 

 This might still be the case even though the substance consumed in 

 respiration was associated with the protoplasm, and continually liberated 

 only to be immediately oxidized. 



The regeneration of the amides produced by metabolism is simply a special 

 case of the chemosynthesis of proteids, and is indirectly influenced to a great 

 extent by the action of light, not merely owing to the fact that by means of the 

 latter the necessary carbohydrates may be produced, but also because light 

 forms an essential condition for the normal performance of many vital activities. 

 Indeed the changes in the shape and in the growth of green parts developed 

 in darkness are necessarily accompanied by corresponding changes in the metabolic 

 activity of the parts affected. The synthetis of proteids will probably be more 

 or less markedly inhibited when pathological conditions of this character are 

 induced in green organs, although respiration and proteid-decomposition may 

 continue with the same or even greater activity. The fact that the regeneration 

 of amides may cease in darkness even when carbohydrates are present, merely 

 indicates that darkness may exercise some such indirect pathological action, and 

 does not necessitate the assumption that the process of regeneration is directly 

 due to the assimilatory action of the light absorbed, as was supposed by O. Miiller 1 . 

 The same regeneration is possible in roots which grow normally in darkness, 

 and according to Monteverde a supply of sugar will partially or completely 

 prevent the accumulation of asparagin in darkened twigs of Syringa ; while 

 Kirioshita finds that the same result is produced in seedlings of So/a grown in 

 darkness and fed with glycerine 2 . It is however certain that the same effect 

 will not be exercised upon all plants 3 , and the most important experiments are 

 those in which the development in darkness is made as normal as possible, either by 

 adopting special modes of treatment or by selecting suitable plants. 



Both Miiller and E. Schulze 4 failed to recognize that metabolism is always 

 determined and regulated by the existent vital activity, and that proteid-synthesis 

 is possible only when all the necessary conditions are fulfilled. External conditions 

 modify the vital activity, and this along with the regulatory mechanism brings it 

 about that in the same cell at one time proteids may be disintegrated, at another 

 reconstructed. In the germination of seeds of Phaseolus, Pisum, &c., the starch 

 and proteids are mobilized and translocated together, but it may be found possible 



1 O. Mu'ller, Versuchsst., 1886, Bd. xxxm, p. 311. 



* Monteverde, Bot. Centralbl., 1891, Bd. XLV, p. 379; Kinoshita, Bull. Coll. Agric., Tokio, 

 1 895, Bd. II, p. 197. 



8 Prianischnikow (Versuchsst., 1896, Bd. XLVI, p. 458) has obtained negative results with seed- 

 lings of Vicia sativa. Hansteen (Ber. d. Bot. Ges., 1896, p. 323) has recently shown that Lemna is 

 able to regenerate proteids from amides in darkness. 



* E. Schulze, Landw. Jahrb., 1880, Bd. ix, p. 52. 



