44 



Introduction to Botany. 



growth of the roots ; if the water is distributed evenly, the 

 roots develop evenly on all sides, but if the conditions are 

 otherwise the roots tend to follow the direction of the 

 greater water supply. 



35. Adventitious Roots. — We have noticed in the growth 

 of seedlings that the first rootlets spring from the primary 



root at definite angles of di- 

 vergence, but that on the stems 

 of ivy and Cuscuta their places 

 of origin are indefinite, — in 

 other words, these roots seem 

 to arise adventitiously. When 

 willow stems are cut off and 

 placed in water, roots are 

 formed in the same manner 

 not far above the cut surface. 

 The ability of plants to form 

 adventitious roots is employed 

 by horticulturists and florists 

 in the propagation of many 

 kinds of plants by the pro- 

 cesses known as layering and cuttage. In this way may 

 be propagated currants, gooseberries, raspberries, grapes, 

 roses, azaleas, fuchsias, etc. (See Fig. i8.) 



36. Roots Defined. — Although roots are called upon to 

 perform various functions, and may be modified in form 

 accordingly, they still have certain characteristics which 

 distinguish them from other plant members. They are 

 members of the plant body of indefinite elongation, pro- 

 tected by a root-cap ; and they never directly bear leaves, 

 although capable of producing adventitious buds. 



Fig. i8. 



Showing the method of Layering. A 

 branch is bent and pegged down 

 and covered with soil. After adven- 

 titious roots have formed on the 

 branch it is severed from its parent 

 stock. After Barry. 



