21 8 Mr, Knight on the Causes which influence 
takes place, and consequently the roots which immediately 
adjoin the trunk of an insulated tree, in an exposed situation, 
become strong and rigid ; whilst they diminish rapidly in bulk, 
as they recede from the trunk, and descend into the ground. 
By this sudden diminution of the bulk of the roots, the pas- 
sage of the descending sap, through their bark, is obstructed; 
and it in consequence generates, and passes into many lateral 
roots ; and these, if the tree be still much agitated by winds, 
assume a similar form, and consequently divide into many 
others. A kind of net-work composed of thick and strong 
roots is thus formed, and the tree is secured from the dangers 
to which its situation would otherwise expose it. 
In a sheltered valley, on the contrary, where a tree is sur- 
rounded and protected by others, and is rarely agitated by 
winds, the roots grow long and slender, like the stem and 
branches, and comparatively much less of the circulating fluid 
is expended in the deposition of alburnum beneath the ground; 
and hence it not unfrequently happens, that a tree, in the 
most sheltered part of a valley, is uprooted ; whilst the ex- 
posed and insulated tree, upon the adjoining mountain, remains 
uninjured by the fury of the storm. 
In all the preceding arrangement, the wisdom of nature, 
and the admirable simplicity of the means it employs, are con- 
spicuously displayed; but I am wholly unable to trace the exist- 
ence of anything like sensation or intellect in the plants: and 
I therefore venture to conclude, that their roots are influenced 
by the immediate operation and contact of surrounding bodies, 
and not by any degrees of sensation and passion analogous to 
those of animal life ; and I reject the latter hypothesis, not 
only because it is founded upon assumptions, which cannot be 
