ADJUSTMENT TO SURROUNDINGS 



143 



136. Correlation among Leaves. — On a vertical and 

 equally illuminated branch, as of maple, the petioles of 

 the lower leaves are longer than those above them, and 

 the stalks of opposite leaves are usually about equal in 



Fig. 102. — Garden nasturtium {Tropaolum majus), showing leaf- 

 mosaic in seedlings. Top view; compare Fig. 95, showing other views of 

 the same seedlings. 



length (Figs. 100 and loi). But on horizontally growing 

 branches, the attitude of the leaves is profoundly altered. 

 The length of the petioles, and their attitude is such as 

 to insure the placing of the blades in positions for the 

 most favorable illumination. This often results in a 

 marked twisting and bending of the leaf-stalks. Blades 



