JACQUES LOEB 



381 



however, collect in the new roots. A closer inspection of the leaves 

 shows that the red pigment collects not only in the lower half of the 

 leaves but also in those notches of the upper part of the leaf where 

 roots or shoots are growing vigorously, thus supporting the view that 

 the flow of sap is directed to rapidly growing organs. While a small 

 amount of red pigment may possibly be visible in a leaf under normal 

 conditions (especially along the edge of a young leaf), a noticeable 

 amount is formed when the amount of water in the leaf is diminished. 



Fig. 5, Two sister leaves, one suspended in moist air, the other dipping with its 

 apex into water. Only the former shows the pigment formation while the latter 

 does not. This result is general and proves that the formation of the reddish 

 pigment is favored by a diminution in the amount of water in the leaf since in 

 the leaves suspended in moist air the ratio of dry to fresh weight is greater than 

 in leaves which dip into water. Duration of experiment, Apr. 2 to Apr. 17, 1919. 



This is shown by a comparison of the two sister leaves in Fig. 5, one 

 of which (the one on the right) dipped with its apex into water while 

 the other (the one to the left) was suspended in moist air. The ratio 

 of dry weight to fresh weight of such leaves is always greater in the 



