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 mycelium 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 mediumin which ,,, 7. — Method, of formation 
the roots live. The soil offering of adventitious branches from 
. . the growth of dormant buds. 
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 
