i6 



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 Chamacyparis 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;'' 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 Zerstorung des Chlorophylls in lebenden Organen. Bot. Zeitg. 32 : 433-439. 



1874- 



- 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 h. la 

 veg6tation, 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 £ertilit6. Compt. rend. Paris 109: 397-400. 1889. 



h This may also be seen in the arbor vitae (Thuja occidentalis) of the northeastern United 

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



