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PHYSIOLOGY. 
BOOK II. 
CHAPTER IV. 
OF THE ROOT. 
’It is the business of the root to absorb nutriment from the 
soil, and to transmit it upwards into the stem and leaves; and 
also to fix the plant firmly in the earth. Although moisture is, 
no doubt, absorbed by the leaves and bark of all, and by the 
stems of many, plants, yet it is certain that the greater part of 
the food of plants is taken up by the roots ; which, hence, are 
not incorrectly considered vegetable mouths. 
But it is not by the whole surface of the root that the 
absorption of nutriment takes place ; it is the spongioles 
almost exclusively to which that office is confided : and hence 
their immense importance in vegetable economy, the absolute 
necessity of preserving them in transplantation, and the certain 
death that often follows their destruction. This has been 
proved in the following manner, by Senebier: — He took a 
radish, and placed it in such a position that the extremity 
only of the root was plunged in water : it remained fresh 
several days. He then bent back the root, so that its extremity 
was curved up to the leaves : he plunged the bent part in 
water, and the plant withered soon ; but it recovered its 
former freshness upon relaxing the curvature, and again 
plunging the extremity of the root into the water. 
This explains why forest trees, with very dense umbrageous 
heads, do not perish of drought in hot summers or dry situa- 
tions, when the earth often becomes mere dust for a consider- 
able distance from their trunk, in consequence of their foliage 
turning off the rain : the fact is obviously that the roots near 
the stem are inactive, and have little or nothing to do as pre- 
servatives of life except by acting as conduits, while the func- 
tions of absorption go on through the spongioles, which, being 
at the extremities of the roots, are placed beyond the influence 
of the branches, and extend wherever moisture is to be found. 
