HOW BIG TREES GROW 39 



Evergreen trees are far less exacting regarding soil 

 and moisture requirements than most deciduous vari- 

 eties. As a rule conifers demand only one-sixth to 

 one-tenth as much moisture and one-quarter to one- 

 half as much fertility, so that pines, spruces, firs, etc., 

 will grow well on soils that would afford poor accom- 

 modations to oaks, maples, beech, etc. 



How a Tree Develops. So much for the general fac- 

 tors required for plants. Now in order that we may 

 clearly understand how a forest develops and its rela- 

 tion to its surroundings, the growth of the individual 

 tree must be studied. 



A tree is composed of roots, stem, branches, and 

 leaves, and for reproducing the species, to the above 

 flower, fruit and seed must be added. 



Roots really serve two purposes, they anchor the 

 tree firmly in position, defying the effects of wind 

 and snow, while at the ends of the roots just back of 

 the tip or growing point are found delicate root hairs, 

 which draw in the moisture and plant food dissolved 

 in the water which surrounds the soil particles. 



The stem anH branches are the framework of the 

 plant which support the leaves; the latter serve as 

 the stomach and lungs at the same time. The soluble 

 salts coming in through the delicate cell walls of the 

 root hairs pass up through the sap wood to the leaves. 

 There the water is combined with oxygen, and carbon 

 dioxide found in the air is taken in through openings 

 "stomata" found on the under side of the leaves. These 

 two ingredients are combined in the presence of a 

 green substance called chlorophyll, found in the leaf 

 cells, to make starch and sugar. 



Any water that is not used by the leaves to manu- 

 facture plant food passes out through the stomata as 



