12 
INTRODUCTORY. 
mantle of delicate threads. However that may be, the fluid 
that is taken up by the roots is not merely water, but water plus 
dissolved mineral matter and nitrogen. At the same time as the 
roots are thus absorbing liquid nutriment, the leaves, pierced with 
thousands of little stomata, or mouths, take in atmospheric air, 
which is compounded chiefly of the gases oxygen and carbon. 
The leaf-cells containing the green colouring matter {chloro- 
phyll) seize hold of the carbon and release the oxygen. The 
carbon is then combined with the fluid from the roots by the 
vital chemistry of the leaves, and is circulated all over the 
system for the sustenance of all the organs and tissues. 
The flowering of the trees varies so greatly that it can only 
be dealt with satisfactorily as each species is described. It may 
be stated, however, that all the true forest trees are wind- 
fertilized, and therefore have inconspicuous greenish blossoms. 
By true forest trees we mean those that alone or slightly mixed 
are capable of forming high forest. The smaller trees, such as 
Crab, Rowan, Cherry’, Blackthorn, Hawthorn, Buckthorn, etc., 
belong more to the open woodland, to the common and the 
hedgerow. These, from their habitat, can be seen singly, and 
therefore can make use of the conspicuous flowers that are 
fertilized by insects. 
