Growth and Form Development 



15 



tips of the roots to the tips of the crown with all its 

 ramification of branches, consists of very loose, thin-walled 

 cell tissues; hence it affords an easy pathway for the growth 

 of the mycehum of wood-destroying fungi. It is along this 

 line of least resistance that the most rapid progress of rot is 

 made, and hence there is need for 

 particular attention to the branch 

 wounds where the fungus enters. 



The root system develops in a 

 manner somewhat similar to the 

 crown, lengthening and ramifying 

 by annual additions and increas- 

 ing in diameter by division and 

 growth of cambium cells. There 

 are, however, differences in devel- 

 opment, due, no doubt, to the 

 difference of the medium in which 

 the roots live. The soil offering 

 more resistance than the air, the 

 ramifications are less regular. Instead of having more or 

 less systematically arranged buds from which new roots 

 may form, irregular growing points may arise on any part 

 of the root where the bark is not too resistant, thus pro- 

 ducing the new growth. The root system is therefore less 

 regular, less symmetrical than the crown system. Never- 

 theless, as we recognize typical forms of crowns like that 

 of the conical conifer, the spreading oak, the vase-shaped 

 elm, so there are typical root systems, which fact has more 

 bearing upon the form of ornamental and shade trees, than 

 is usually recognized. 



Although the root systems of most trees are very adaptive, 

 there is a limit to the adaptation, and, as the trees grow 

 older, the difficulty of adaptation grows greater, and shows 



Fig. 7. — Method of formation 

 of adventitious branches from 

 the growth of dormant buds. 



