LECT. V.] THE ROOT. 205 



is, in every instance, downwards, depending on 

 causes which have not yet been ascertained *; and 

 although roots, during their growth, assume va- 

 rious directions, which invariably occur in the 

 same kinds of roots, yet, that circumstances con- 

 nected with their mode of growth, produce devia- 

 tions, and affect the uniformity which might 

 otherwise be expected. But many roots not only 

 vary from their natural direction, but even change 

 their characteristic figure, owing to circumstances 

 connected with the state of the soil : thus, insu- 

 lated trees, that are much agitated by the wind, 

 have strong lateral roots, forming a kind of net- 

 work that adheres firmly to the earth ; whilst 

 the same description of trees, growing in a forest, 

 has long slender tapering roots. This diversity 

 may be thus explained : when a tree stands alone, 

 the soil near the surface is partially loosened by 

 the agitation of the tree by the wind, and conse- 

 quently less opposition is afforded to the extension 

 of the lateral branches of the root, than the un- 

 moved ground offers to that of its perpendicular 

 caudex ; whereas, when a tree grows in a forest, 

 the mechanical obstacles offered to the extension 

 of the lateral roots by the neighbouring roots, ex- 



* The different opinion^ that have been hazarded on this 

 subject shall be noticed, when we take under our consideration 

 the germination of seeds. 



