28 



Handbook of Nature-Study 



The upturned roots of a white pine; a part of a stump fence 



a century old. 



To understand how firm a base the roots form to hold up the tall trunk, 

 we need to see an uprooted tree. The great roots seem to be molded to take 



firm grasp upon 

 the soil. It is 

 interesting to 

 study some of 

 the "stump 

 fences" which 

 were made by 

 our forefathers, 

 who uprooted 

 the white pines 

 when the land 

 was cleared of 

 the primeval for- 

 est, and made 

 fences of their 

 widespreading 

 but rather shal- 

 low extending 

 roots. Many of 

 these fences 

 stand to-day 



with branching, out-reaching roots, white and weather-worn, but still 

 staunch and massive as if in memory of their strong grasp upon the soil 

 of the wilderness. 



The trunk, or bole, or stem of the tree has also two chief offices: It 

 holds the branches aloft, rising to a sufficient height in the forest so that its 

 head shall push through the leaf canopy and expose the leaves to the sun- 

 light. It also is a channel by which the water containing the food surges 

 from root to leaf and back again through each growing part. The branches 

 are divisions of the trunk, and have the same work to do. 



In cross-section, the tree trunk shows on the outside the layer of protec- 

 tive bark; next to this comes the cambium layer, which is the vital part of 

 the trunk; it builds on its outside a layer of bark, and on its inside a layer 

 of wood around the trunk. Just within the cambium layer is a lighter 

 colored portion of the trunk, which is called the sap-wood because it is filled 

 with sap which moves up and down its cells in a mysterious manner; the 

 sap-wood consists of the more recent annual rings of growth. Within the 

 sap-wood are concentric rings to the very center or pith ; this portion is 

 usually darker in color and is called the heartwood; it no longer has 

 anything to do with the life of the tree, but simply gives to it strength and 

 staunchness. The larger branches, if cut across, show the same structure 

 as the trunk, the bark on the outside, the cambium layer next, and 

 within this the rings of annual growth. Even the smaller branches and 

 twigs show similar structure, but they are young and have not attained 

 many annual rings. 



The leaves are borne on the outermost parts of the tree. A leaf 

 cannot grow, and if it could would be of no use, unless it can be reached 

 by the sunlight. Therefore the trunk lifts the branches aloft, and 

 the branches hold the twigs far out, and the twigs divide into the 

 fine spray, so as to spread the leaves and hold them out into the sunshine. 



