THE PHYSIOLOGY OF SOWING SEEDS. 621 
the parts of the plant above the soil. If the 
soil be friable and porous, as they descend the 
more numerous are the fibrils which they emit 
among these pores, and the more spongioles 
thence brought into action, and greater supplies 
sent up to the plant. The vigour of the plant, 
therefore, proportionably increases, the root par- 
ticipates in this vigour, pushes downward more 
rapidly, and sends off laterally more ramifications 
in its course, so that such a supply of material is 
sent up to the building, that the first foundation 
does not require all; wings are added, in offsets, 
or the stooling of new stems, these send down 
their roots in a similar manner, with similar 
action, and similar results; a repetition of the 
same goes on until the space allowed the plant to 
grow in is filled up, or the stores in the soil 
drawn upon to the full amount. And whatever 
interferes with this stooling, whether weeds and 
grasses, or even grain plants, or too great a 
number themselves, checks vegetation ; and con- 
sequently diminishes produce. 
But if a full aeration be essential zm the soil, 
for the multiplication of roots a full areation on 
the soil is equally essential. Upon a free circu- 
lation of air around the blades and culms of the 
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