CHAPTER VII. 



SOME FUNDAMENTAL PRINCIPLES OF PLANT GROWTH. 



The roots of plants are made up of several distinct parts. 

 The main central root is termed the tap root when it extends 

 directly downward into the earth, as in the roots of Bur Oak 

 and Black Walnut. When a plant has several spreading roots 

 it is said to have surface roots, but such roots may sometimes 

 divide and go deep into the ground; for example, the roots of 

 the Red Oak and White Pine. Root fibres or rootlets is the 

 term used for the smaller division of roots. The foregoing 

 roots have hard bark, and do not feed the plant. They do little 

 more than anchor it in place. The roots feed through what 

 are known as the root hairs, which are soft, fresh, young roots 

 generally white in color. 



The collar or crown of a plant is that portion where the 

 roots and top unite. It is close to the surface of the ground. 

 This portion of the tree is frequently injur-ed by borers, by ice 

 and in other ways. It is a good plan, especially in the case of 

 young trees, to protect them in winter with a bank of earth 

 around the collar. 



The stems of plants may be annual, as in the case of many 

 garden plants; biennial, as in the case of the raspberry and 

 blackberry, and perennial, as in the currants, gooseberries and 

 fruit trees. Runners are creeping stems, as in the case of the 

 strawberry. Suckers are stems springing up from roots or 

 underground stems. Thorns are modified branches and live for 

 indefinite periods white prickles, like those on the gooseberry, 

 are modifications of the bark and live but one year. 



The bark covers the whole exterior of the trunk, branches 

 and roots and serves as a protection. It is made up of two 

 parts, the outer or corky layer which is dead bark, and the in- 

 ner, or live bark. These vary much in appearance and thickness 

 on different kinds of trees. For instance, on the White Birch 

 the corky layer is pure white, very thin and tough, while on 

 our White Pine it is very dark brown and often an inch or 



