246 LEAVES 



found to be already healed. The absciss layer is respon- 

 sible for this. It often forms a healing scar even before 

 the leaf falls off. The cells of this layer differ from ad- 

 joining cells in that they are more turgid and have 

 thinner walls. Cork sometimes appears in them, and 

 forms the healing scar. 



In temperate regions the colors of leaves in autumn form 

 one of the most striking beauties of nature. The reds and 

 golds of the woods in October delight us as much as their 

 soft green of early spring. Maples and oaks, the dogwood 

 and the sumach, give us masses of color which make us 

 exclaim with pleasure. Just what it is that causes this 

 change in color cannot be expressed in a single word. It 

 is common to hear that frost does it, but this is disproved 

 by the fact that the bright colors often come before the first 

 frost. Sometimes a bright-colored branch is found in the 

 woods in midsummer, and young leaves often show a tend- 

 ency to redness much like that which they show in the fall 

 when they are old. It appears that the cause of the colors 

 may be anything which reduces the activity of the leaves. 

 It is not surprising that an early frost has been considered 

 the principal cause. Sometimes it is the principal cause, 

 for it may be the first thing to interfere with the work of 

 the leaves. 



Redness in leaves is produced by certain substances 

 called anthocyans. The anthocyans are found in solution 

 in the cell sap. They seem to appear when sugar is abun- 

 dant. Redness has been induced in leaves by growing plants 

 in solutions of sugar. It has been suggested that the 

 absciss layer, which is usually full of starch, checks the 

 migration of sugar out of the leaf and so indirectly causes 

 the shades of red to appear. 



