1 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, 1 the conifer Chamcecyparis obtusa is especially interesting in this 

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

 son, while shaded ones remain green; 71 at the margin between the shaded and un- 

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



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

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

 in a leaf in the autumn, while it is still green, so that the chlorophyll 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. 3 Without iron, plants remain bright yellow, thus suffering from 

 chlorosis. 



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

 by an incision. (After 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 1 was able to show that the absence of necessary mineral salts in the 

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



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

 1874. 



2 Stahl, Ernst, Zur Biologie des Chlorophylls; Laubfarbe und Himmelslicht, Vergilbung und Etiole- 

 ment. Jena, 1909. 



3 Gris, Eusebe, Nouvelles experiences sur Taction des composes ferrugineux solubles, appliques a la 

 vegetation, et specialement au traitement de la Chlorose et de la debilite des plantes. Compt. rend. Paris 

 19: 1118-1119. 1844. Molisch, Hans, Die pflanze in ihren Beziehungen zum Eisen. Eine physiologische 

 Studie. Jena, 1892. 



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

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



л This may also be seen in the arbor vitae (Thuja occidentals s) of the northeastern United 

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



