THE BROWNING OF THE LEAVES 239 



solution. Lo, the circle that has been covered 

 with the cork remains white, and only the rest goes 

 black. The circle finding itself in the dark 

 ceased to secrete starch, and sent in what it had 

 already made to the midrib, and thence to the 

 main plant for its common needs. 



So in the autumn, and let who will put it down 

 to mere reflex action in response to failing light. 

 The days are as long, the sun as near, the air and 

 soil as warm as in April, when every leaf was hard 

 at work making green. But something makes 

 the trees carry out a policy, the utility of which 

 will be manifest some weeks hence. Every possible 

 grain of starch is converted by the vegetable 

 saliva into sugar and carried back into the twigs, 

 the trunk, or even the roots. When the last 

 available grain has gone in, a barricade is set up 

 between twig and leaf, a division neatly sealed 

 with cork made between them, and the next 

 breeze casts the empty leaf down. In the case of 

 compound leaves, like those of the chestnut and 

 the Virginia creeper, each leaflet is thus cut off, 

 and a little later, the convoy having passed the 

 leaf-stalk, that, too, is cut off and thrown away. 



But why, when the leaves are empty, are they 

 not white as in the case of our summer experiment ? 

 ,We bleached that summer leaf by taking away 

 its chlorophyl or green starch-collecting matter. 

 In the autumn leaf, the dregs of the chlorophyl 

 remain as detached units cut off from the retreat 

 hanging along the veins and the sides of the cells 



