48 PLAKT LIFE GIST THE FAftM. 



ing a bean to germinate on the surfafce 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 oif 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 form 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 " 



