620 THE PHYSIOLOGY OF SOWING SEEDS. 
matter within the soil. But if there be a great 
extent of root, this vigour has been occasioned 
by their greater range of action. In the former 
instance, the material has been near at hand, and 
fewer labourers were therefore required to build 
the structure. In the latter the material had to 
be brought from a distance, and, therefore, more 
hands had to be employed. But were the 
two soils brought into action to their full 
limits, then a much nobler structure might be 
raised by the first than by the second. Much, 
then, depends upon culture. The capacities of 
soils have to be brought out, in order that 
vegetation may flourish to the utmost; and this 
can only be done by what has been urged again 
and again as essential, a thorough loosening and 
pulverising, and consequent aeration of as much 
soil as exists, or as the implements of husbandry 
are competent for. 
The natural tendency of subterraneous roots, 
is to shun the light and direct themselves down- 
ward into the soil; their natural function is, as 
they thus descend into the soil, to absorb from it 
by the extreme tips of the fibrils, or spongioles, 
the fluid around them with the gaseous and other 
matter it may contain, and transmit it upward to 
