EFFECT OF ACCUMULATION OF ASSIMILATORY PRODUCTS 323 



when removed from the parent plant, and Saposchnikoff showed by more 

 detailed observations that the assimilatory products (sugar, starch and 

 proteids) cannot increase beyond a certain amount in the leaf of Vitis. In 

 all regulatory processes, any over-accumulation not merely acts mechanically, 

 but also exerts an inhibitory stimulating action upon the chloroplastid, 

 rendering it temporarily inactive, as was directly shown by Ewart's observa- 

 tions, and this condition may persist for a time even though the assimilatory 

 products are partially removed (cf. Sect. 58). 



Under normal conditions no marked effect upon the assimilatory 

 activity is noticeable, for the continuous removal of the assimilatory products 

 ensures that no excessive accumulation occurs during the day, while during 

 a warm night the starch or sugar disappears entirely or almost entirely 

 from the leaves of most plants, so that at sunrise they contain much less 

 carbohydrate than at nightfall. The translocation continues during both day 

 and night, and moreover exhibits a certain periodicity 1 . Starch disappears 

 only when translocation is more active than carbon dioxide assimilation, and 

 the activity of translocation is directly or indirectly influenced by various 

 external conditions. Any agency which affects the rate of consumption 

 of the assimilatory products will also affect the translocatory activity, and 

 hence may indirectly influence the assimilatory activity of the chloroplastid. 

 In every case, therefore, it is necessary to determine precisely the various 

 factors concerned in producing the result observed, and since all plants 

 do not necessarily react in precisely the same manner, it is not .surprising 

 to find that the presence of common salt causes the percentage of starch to 

 increase in some plants but to diminish in others, evidently because the salt 

 influences the translocatory and assimilatory activities to relatively different 

 extents. Temperature, oxygen, amount of water, &c., exert the same 

 general effect as they do upon all other vital activities 2 . 



The assimilatory activity cannot be determined by estimating the 

 increase in the dry weight of the leaf, for any increase simply represents 

 the extent to which photosynthetic assimilation is more active than translo- 

 cation and respiration. The latter causes the consumption of from ^\ to --$ 

 of the organic material \vhich a leaf produces under optimal illumination 3 . 

 Hence it is only when assimilation is very active that carbohydrate? 



1 Sachs, Arb. d. Bot. Inst. in \Yiirzburg, 1884, Bd. Ill, p. 7 ; Muller-Thurgau, Landw. Jahrb., 

 1885, Bd. xiv, p. 809; Saposchnikoff, Ber. d. Bot. Ges., 1890, p. 235; Costerns, Ann. d. Jard. 

 bot. d. Buitenzorg, 1894. Bd. xii, p. 73. Cf. also Mer, Beihefte z. Bot. Centralbl., 1891, Bd. I, 

 p. 184. [Costerus (I.e.) has shown that in most tropical plants the starch is translocated most 

 actively during the early morning hours.] 



2 Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. n, p. 291 ; Nadson, Bot. Centralbl., 



1890, Bd. XLII, p. 48; Lesage, Compt. rend., 1891, T. cxn, pp. 672, 891 ; Klebs, Bot. Zeitung, 



1891, p. 809; Schimper, Indo-Malayische Strandflora, 1891, p. 26; Stange, Bot. Zeitung, 1892, p. 

 394 ; Richter, Flora, 1892, p. 55 ; Stahl, Bot. Zeitung, 1894, p. 133. Effect of oxygen : Wortmann, 

 Bot. Zeitung, 1890. p. 662. 



3 Kreusler, Landw. Jahrb.. 1885. Bd. xiv. p. 952. (Cf. Sect. 95.) 



V 2 



