cess, for it seems evident that it cannot take 

 place without light and the peculiar green 

 substance which gives the characteristic 

 color to leaves. With the help of light and 

 this green coloring substance, known as 

 "chlorophyll," the living substance in the 

 leaves is able to do this marvelous work. 



The food thus manufactured is distributed 

 throughout the tree, either to be used 

 wherever growth is going on, or to be stored 

 up. While we may say that there is an 

 "ascending current " of sap through the sap 

 wood, it is an error to say that there is a 

 "descending current." The movement of 

 prepared food has no definite channel, but it 

 is drawn in every direction wherever needed. 



If we now consider the parts of a tree all 

 together, we may be able to get some notion 

 of the meaning of their positions. The 

 roots must be related to the soil to secure 

 anchorage and raw material for food manu- 

 facture. The leaves must be related to the 

 air and light to secure more raw material 

 and help in doing their important work of 

 food manufacture. The stem is simply to 

 carry the leaves well up into the air and 

 sunshine, and has no meaning except as it 

 is related to the work of the leaves. In thus 

 widely separating the roots and the leaves, 

 the stem must act as a channel of communi- 

 cation between them. 



In the tree trunks with which we are 

 familiar, everyone has observed the concen- 

 tric rings of wood that appear in a cross- 

 section. These are usually spoken of as 

 " annual rings," with the idea that one ring 

 is made each 3'ear. In consequence of this 

 it is the habit to estimate the age of a tree by 

 counting these rings. Not infrequently it 

 happens, however, that more than one ring 

 may be made in a year, as a ring represents 

 a single season of growth, and there may be 

 more than one season of growth during a 

 single year. It is much better to call them 

 "growth rings," and to recognize the fact 

 that by counting them we may be overesti- 

 mating the age of a tree- 



One of the most noticeable things about 



101 



the principal trees of our temperate climate is 

 that they " shed " their leaves every year, 

 being covered with foliage during the grow- 

 ing season and bare during the winter. This 

 is known as the "deciduous" habit, and 

 such trees are called deciduous trees, in dis- 

 tinction from ' ' evergreen ' ' trees. This is 

 really a habit, brought about by the con- 

 ditions in which trees of temperate climates 

 must live. The leaves of such trees are broad 

 and thin, fitted for very active work. When 

 the winter comes, they would be entirely 

 unable to endure it. The tree might pro- 

 tect them by giving them narrow forms and 

 thick walls (as in pines), but it would be at 

 the expense of activity during the growing 

 season. It is more economical for the tree 

 to make an entirely new set of leaves each 

 year than to protect the old ones. 



Perhaps the most noticeable feature in 

 connection with the fall of the leaves is that 

 so many of them take on a rich coloration. 

 Our mixed American forest is the most 

 brilliantly colored autumnal forest in the 

 world, and there can be no landscapes richer 

 in color than those which include such a 

 forest. While all this should appeal to our 

 sense of the beautiful, it should raise the 

 question as to what it means in the life of 

 the trees. We are not at all sure that we 

 know, for we cannot as yet explain the con- 

 ditions which cause the colors to be pro- 

 duced. We observe that they occur towards- 

 the end of the activity of the leaf, but that 

 they are necessarily associated with cold, or 

 drought, or certain outside conditions, is not 

 at all clear. The colors are various shades 

 of red and yellow, sometimes pure, some- 

 times mixed. It has been recently suggested 

 that the red color is to serve as a protection. 

 It is known that before the fall of the leaf 

 the living substances are gradually with- 

 drawn into the permanent parts of the tree, 

 and that when these living parts cease to 

 work they are peculiarly helpless. At this 

 unprotected period the red appears, and this 

 color absorbs enough heat from the light to 

 raise the temperature, and so the needed pro- 



