LESSON ON LEAVES 



PROF. H. L. HUTT, B. S. A. 



O. A. C, GUELPH, ONT. 



TREES and shrubs may be divided into 

 two classes, depending upon whether 

 they retain or annually shed their 

 leaves. Those which retain their leaves are 

 evergreens, while those which shed their 

 leaves are deciduous. In this country our 

 commonest evergreens are the pines, spruces, 

 cedars, etc., while all of our fruit trees are 

 deciduous. In warmer climes, where the 

 tropical fruits are grown, even the fruit 

 trees, such as orange and lemon, are ever- 

 greens. 



Leaves afford an interesting subject for 

 study, not only because of their great var- 

 iety, but because of their wonderful modifi- 

 cations of form to suit varied conditions. 

 This part of the subject, however, we must 

 leave the reader to study for himself. At 

 present, we shall deal more particularly with 

 a few of the most important functions which 

 the leaves perform in the economy of plant 

 growth. 



THE STRUCTURE OF A LEAF 



A leaf is usually made up of two principal 

 parts, the broad expanded part called the 

 blade; and the stalk which supports it, 

 known as the leaf-stalk or petiole. The 

 blade is one of Nature's adaptations for the 

 purpose of exposing as much surface as 

 possible to the action of sunlight, for al- 

 though a leaf may be small in itself, the 

 area exposed by the foliage of a large apple 

 tree in full leaf may amount to several acres. 



The petiole or leaf-stalk, is not always an 

 essential part of the leaf, for in some cases 

 it is absent, as in the Honeysuckle, in which 

 the blade rests directly upon the branch. 



If, for instance, we examine a maple leaf, 

 it will be seen that the petiole divides at its 

 upper end into a number of parts, and these 

 divide again and again into smaller parts 

 forming what are usually spoken of as the 

 nerves or veins of the leaf. With the peti- 

 ole, they make up the skeleton or framework 



