FAMILIAR TREES. 



INTRODUCTION. 



TKEES are defined as perennial plants with 

 a principal stem of some considerable dia- 

 meter, rising from the ground and forming wood. 

 Their woodiness distinguishes them from all herbs, 

 and their one principal stem from shrubs. 



• Like all other highly-organised green plants, trees 

 grow by means of food derived from the air by their 

 leaves and from the soil by their rootlets. For 

 this reason it is advantageous for the tree to 

 expose as large a leaf-surface as possible to light 

 and air; and thus we find not only its stem in 

 most cases repeatedly branched, but also its leaves 

 so disposed as to overlap each other to the least 

 possible extent. The multitude of rootlets have 

 some power of dissolving saline substances in the 

 soil, and these they absorb, with an abundance of 

 water, as an extremely dilute solution. By a com- 

 bination of a force-pump action in the roots and 

 suction exerted by the constant evaporation of 

 water through the leaves, this Avatery fluid rises 

 rapidly to the topmost leaf of the tallest tree, and 

 in the celLs of the leaves — the laboratories of the 

 plant — it combines with the carbonaceous matter 

 taken in from the air. In obtaining nitrogen from 

 i 



