1 6 PHYSIOLOGY OF NUTRITION 



The autumn coloration of leaves is dependent upon light and upon the tem- 

 perature of the air; chlorophyll is decomposed by sunlight in autumn, while its 

 re-formation is hindered by the low temperatures then prevailing. According 

 to Batalin.i ti^g conifer Chamacyparis ohtusa is especiaUy interesting in this 

 connection. Branches in sunshine have a golden-yellow color in the cold sea- 

 son, whHe shaded ones remain green;* at the margin between the shaded and un- 

 shaded regions the different colors may often be seen in neighboring ceUs. 



The products of chlorophyll decomposition do not remain in the leaf but dif- 

 fuse away.2 This is shown by the foUowing experiment: if an incision is made 

 in a leaf in the autumn, whUe it is stUl green, so that the chlorophyU decomposi- 

 tion-products are prevented from diffusing away, the part of the leaf above the 

 cut remains green .while the other parts turn yellow (Fig. 9). 



The presence of iron is a third condition necessary for the formation of 

 chlorophyll. 2 Without iron, plants remain bright yeUow, thus suffering from 

 chlorosis. 



Fig. 9. — Gingko leaf in which autumnal coloration has been prevented in the upper part, 



by an incision. (A//er Stahl.) 



The presence of oxygen is an additional condition necessary for greening. !| 

 Etiolated leaves in an oxygen-free chamber remain yellow, even in light. This 

 is also true when the amount of oxygen is small; greening demands an excess 

 of this gas. 



Ville* was able to show that the absence of necessary mineral salts in the 

 soU results in the diminution of the chlorophyll and carotin contents of leaves. 



1 Batalin, A., Ueber die ZerstSrung des Chlorophylls in lebenden Organen. Bot. Zeitg. 32 : 433-439. % 

 1874- ,' 



» Stahl, Ernst, Zur Biologie des Chlorophylls; Laubfarbe und Himmelslioht, Vergilbung und Etiole- ,- 

 ment. Jena, 1909. 



3 Oris, Eusebe, Nouvelles experiences sur Taction des composes ferrugineux solubles, appliques ^ la 

 v6g6tation, et sp6cialement au traitement de la chlorose et de la d€bilit^ des plantes. Compt. rend. Paris 

 19:1118-1119. 1844. Molisch, Hans, Die pflanze in ihren Beziehungen zum ^en. Bine physiologischa j 

 Studie. Jena, 1892. '' 1 



' Ville, Georges, Recherches sur les relations qui existent entre la couleur des plantes et la richesse des 

 terres en agents de fertiht6. Compt rend. Paris 109: 397-400. 1889. 



* This may also be seen in the [arbor vitas {Thuja occidentalis) of the northeastern 

 United States in very cold, bright winter weather. — Ed. 



