426 On the Direction of the Growth of Roots. 



the growth of the roots was retarded by « ant of moisture, 

 the contignity of water, in the adjoining mould, i hough not 

 apparent Iv in actual (;ontaci with them, operated benefi- 

 ciallv : but I had reason to suspect that the growth of roots 

 was, under the<e cireiinistaiices, promoted by actual con- 

 tact with the detached and fugitive particles of the decom- 

 posing body, and of the evaporating water. 



The growth and forms assumed by the roots of trees, of 

 every species, are to a great extent dependent upon tlie 

 quantity of motion which their stems and branches receive 

 from winds; for the efiects of motion upon the growth of 

 the root, and of the trunk and branches, wiiich I have de- 

 scribed in a former memoir, are perfectly similar*. What- 

 ever part of a root is moved and bent by winds, or other 

 causes, an increased deposition of alhurnous matter upon 

 that part soon takes place, and consequentiv the roots which 

 immediately adjoin the trunk of an insulated tree, in an 

 exposed situation, become strong and rigid; v\hilsl 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 passage of the descending sap, 

 through their bnrk, is obstructed; and it in coittequence 

 generates, and passes into many lateral roots; and these, if 

 the tree be still much agitated by winds, assume a simdar 

 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 circulatmg 

 fluid is expended in the deposition of alburnum beneath the 

 ground ; and hence it not \infrequcnlly happens that a 

 tree, in the most sheltered part of a valley, i". uprooted ; 

 whilst the exposed and insidated tree, upon the adjoining 

 mountain, remains uninjured by the fury of the storm. 



In all the preceding arrantiement, the wisdom of nature, 

 and the admirable simplicity of the means it employs, are 

 conspicuously displaved ; but I am wholly unable to trace 

 the existence of any thing like sensation or intellect in the 

 plants: and I t!,erefore venture to conclude, thai their roots 

 are influenced bv the immediate operation and contact of 

 syrrounding bodies, and not by any degrees of sensation 



* Phil. Trans, 180:3, p. 7. 



and 



