CHAPTER V 



LEAVES 



For three thousand years leaves were more used in the orderly 

 arrangement of plants than any other organs. It was only after 

 the structure and functions of flowers became well known that 

 these and the fruits developed from them began to be regarded 

 as the principal parts of plants for purposes of classification. 

 It is interesting to note that pomologists are now making a new 

 appeal to leaves for aid in classifying. Shaw, of Massachusetts, 

 has found that most fruit-trees can be identified and classified 

 by leaves alone. While, therefore, classifying by foliage never 

 can have the value to systematists it once possessed, it is of great 

 use, especially to pomologists. 



43. An arbitrary definition of leaf. — Leaves have so many 

 offices, functions, types, and disguises, that they are almost im- 

 possible to define precisely. However, leaves are comparatively 

 simple as they exist in pomological plants, especially for pur- 

 poses of classification, so that an easy definition can be given 

 which will suffice. A leaf is a lateral outgrowth of a stem, 

 produced in a definite succession from growing points of the 

 stem. In all hardy fruits they are flattened structures and 

 bear buds in their axils. Their growth differs from that of 

 stems and roots in being definite and of short duration, while 

 that of the latter is indefinite in dimensions and in duration. 

 Stems and roots develop buds as lateral appendages, while 

 leaves seldom do so normally. In hardy fruits the leaf embraces 

 the new branch in its axil. Both leaf and branch are borne at 

 the nodes of stems. 



44. Kinds of leaves. — It may be helpful in obtaining as clear 

 an idea of leaves as possible to mention the various kinds, even 

 though but few of the modifications of common leaves are found 

 in hardy fruits. The typical flat green organ is distinguished 

 as a foliage-leaf. Its chief function is that of food-making. The 



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