DIEECTIOS" O^ THE GROWTH OF ROOTS. 377 



except by actual contact of the injurious substances. The Focrd and mois- 

 growth of their fibrous lateral roots was, however, obr ^"'j^g^^^^^^'^^'^j. 

 Tionsly accelerated, Avhen their points approached any to promote 

 considerable quantity of decomposing vegetable or animal ^'°^^' ^' 

 matter: and when the growth of the roots Avas retarded by 

 want of moisture, the contiguity of water, in the adjoin- 

 ing mould, though not apparently in actual contact with 

 them, operated beneficially : but I had reason to suspect, 

 that the growth of roots was, under these circumstances, 

 promoted by actual contact with the detached and fugitive 

 particles of the decomposing body, and of the evaporating 

 water. 



The growth and forms assumed by the roots of treeSj of dowth and 

 pvery species, are, to a great extent, dependent upon the niodified^y^the 



quantity of motion, which their stems and brancius receive motion im- 



, pressed on ' 

 tree by winds. 



from winds ; for the effects of motion upon the growth ofF*^ 



the root, and of the trunk and branches, which 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 alburnous matter upon 

 that part soon takes place; and consequently the root^ 

 which immediately adjoin the trunk of an insulated tree, in 

 an exposed situation, become strong and rigid; while they 

 diminish rapidly in bulk, as they recede from the trunk, 

 and descend into the ground. By this sudden diniinution^ence trees 



of the bulk of the roots, the passage of the descending"^"*' ^^Po*^'^ 



,,.,,., , 1 • . rare rendered 



sap, through theirbark, is obstructed ; and itm consequence more securej 



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 while sheltered 

 surrounded aud protected by others, and is rarelyagitated^Q'^*^^^^^^^ °"'^ 

 by Minds, the roots grow long and slender, like the stem slender roots. 

 and branches, and comparatively much less of the circulat- 

 ing fluid is expended in the deposition of alburnum be- 



* Phil. Trans. 1803, p. 7. 



neath 



