158 ON TOE DIRECTION 



I have drawn*. But the fibrous roots of plants, being much less succu- 

 lent, though not uninfluenced in the directions they take by gravitation, 

 are, to a great extent, obedient to other laws, and are generally found to 

 extend themselves most rapidly, and to the greatest length, in whatever 

 direction the soil is most favourable : whence many naturalists have been 

 disposed to believe that these are guided by some degrees of feeling and 

 perception, analogous to those of animal life. 



I shall proceed to state some of the facts upon which this hypothesis 

 has been founded, and others which have occurred in the course of my 

 own experience, and which are favourable to it ; after which I shall 

 endeavour to trace the effects observed to the operation of different 

 causes. 



When a tree which requires much moisture has sprung up, or been 

 planted, in a dry soil in the vicinity of water, it has been observed that 

 much the largest portion of its roots has been directed towards the water ; 

 and that when a tree of a different species, and which requires a dry soil, 

 has been placed in a similar situation, it has appeared, in the direction 

 given to its roots, to have avoided the water and moist soil. 



A tree growing upon a wall, at some distance from the ground, and 

 consequently ill supplied with food and water, has also been observed to 

 adapt its habits to its situation, and to make very singular and well- 

 directed efforts to reach the soil beneath, by means of its roots*f. Dur- 

 ing the period in which it is making such efforts, little addition is made to 

 its branches, and almost the whole powers of the plant appear to be 

 directed to the growth of one or more of its principal roots. To these 

 much is in consequence annually added, and they proceed perpendicularly 

 towards the earth, unless made to deviate by some opposing body : and 

 as soon as the roots have attached themselves to the soil, the branches 

 grow with vigour and rapidity, and the plant assumes the ordinary habits 

 of its species. 



Duhamel caused two trenches to be made so as to intersect each other 

 at right angles, and a tree to be planted at the point of intersection ; 

 and taking up this tree some years afterwards, he found that the roots 

 had almost wholly confined themselves to the trenches, in which the soil 

 of the former surface must have been buried. 



A trench which was twenty feet long, six wide, and about two deep, 

 was prepared in my garden, in the bottom of which trench was placed a 

 layer, about six inches deep, of very rich mould, incorporated with much 

 fresh vegetable matter. This was covered, eighteen inches deep, with 



* See above, No. VII. f Smith's Introduction to Botany. 



