48 ARBOR DAY ITS HISTORY AND OBSERVANCE. 



a close resemblance among the leaves of a given tree, so that one 

 familiar with trees would not be in doubt of their belonging to the 

 same tree, though he should see them only when detached, yet there 

 is more or less variation, some subtle difference in the notching or curv- 

 ing of the leaf edge perhaps, so that each leaf has a form of its own. 

 These differences of shape in the leaves are a constant source of beauty. 



What a variety of size also have the leaves, from those of the birches 

 and willows to those of the sycamores, the catalpas, and the paulownias. 

 On the same tree also the leaves vary in size, those nearest the ground 

 and nearest the trunk being usually larger than those more remote. 

 How different as to beauty would the trees be if their leaves were all of 

 the same size; how much less pleasing to the sight. 



Then, what a wide difference is there in the position of the leaves on 

 the trees and their relative adjustment to each other ! Sometimes they 

 grow singly, sometimes in pairs, sometimes in whorls or clusters. Some 

 droop, others spread horizontally, while others still are more or less 

 erect. The leaves of some trees cling close to the branches, others are 

 connected with the branches by stems of various length and so are capa- 

 ble of greater or less movement. The leaves of poplars and aspens 

 have a peculiarly flattened stem, by reason of which the slightest breath 

 of wind puts them in motion. 



These are some of the most obvious characteristics of the leaves, by 

 which also they are made the source of so much of the beauty of the 

 world in which we live. It will be a source of much pleasure to any- 

 one who will begin now, in the season of swelling buds and opening 

 leaves, to watch the leaves as they unfold and notice their various forms 

 and colors and compare them one with another. There is no better 

 way of gaining valuable knowledge of trees than this, for the trees are 

 known by their leaves as well as by their fruits. 



But let us turn now from their outward appearance and consider 

 what is done by them, for the leaves are among the great workers of 

 the world, or, if we may not speak of them as workers, a most impor- 

 tant work is done in or by means of them, a work upon which our own 

 life depends and that of all the living tribes around us. 



Every leaf is a laboratory, in which, by the help of that great 

 magician, the sun, most wonderful changes and transformations are 

 wrought. By the aid of the sun the crude sap which is taken up from 

 the ground is converted by the leaves into a substance which goes to 

 build up every part of the tree and causes it to grow larger from year 

 to year; so that instead of the tree making the leaves, as we commonly 

 think, the leaves really make the tree. 



Leaves, like other parts of the plant or tree, are composed of cells 

 and also of woody material. The ribs and veins of the leaves are the 

 woody part. By their stiffness they keep the leaves spread out so that 

 the sun can act upon them fully, and they prevent them also from being 

 broken and destroyed by the winds, as they otherwise would be. They 



