48 PLANT LIFE ON THE FARM, 
ing a bean to germinate on the surface of wet moss. It 
will thus also be seen that the actual area in which 
growth in length is going on is very small, and that its 
greatest activity is not exactly at the extreme point, but 
a little above it, between it and the point where the root- 
hairs begin to emerge. There is, then, in the growing 
root—first, at the extreme tip a root-cap or shield, con- 
stantly renewed from within by the growth of the cells 
above or within it ; then a region of very limited extent, 
devoted to the growth in length of the root; and above 
that a portion, usually but not always, provided with 
root-hairs, and which is especially told off to fulfil the 
duties of absorption. 
As the upper, thicker part of the root is relatively 
fixed, it will be seen how the fine root fibrils are, by the 
situation of their growing point, enabled to push their 
way, by constant renewal at their growing point, in 
amongst the particles of the soil when the conditions are 
favorable. . 
Growth of the Stem.—In the case of the stem and. 
branches, the growing points, by whose agency increase 
in length takes place, are placed at the summit of the 
stem or of its subdivisions, the branches. The growing 
points then fornf the substance of the ‘ buds,” which are 
either invested by leaf-scales as protectors and stores of 
nourishment, as in the case of bulb-scales, or by perfect 
leaves. The increase in the thickness of stems takes 
place also by means of the growing tissue or cambium, 
the situation of which is different in the two main groups 
of “ Exogens” and “‘ Endogens.” 
To the former series belong all our trees and shrubs, 
the clovers, beet-roots, turnips, and the vast majority of 
plants which have the veins of their leaves disposed in a 
network. In these plants the woody bundles of which 
the stem is principally made up consist of “‘ wood cells ” 
