the Direction of the Groivlh of Roots. 421 



k has been o'nscrved, that much ihe largest portion of its 

 roots has been directed towards the water; and that when 

 a tree of a ditlcrtiU species, and which requires a dry soil, 

 has been placed in a similar siuiation, it has appeared, in 

 the directi.a given to its roots, to have avoided the water 

 and moist soil. 



A tree growiiig upon a wall, at some distance from the 

 ground, and coiibi^quen'Jv i!! supplied with food and water, 

 has also been observed to adapt its habits to its situation, 

 and to make verv singular and well directed efforts to reach 

 the soil beneath, by means of its roots'"". During 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. 



Du Hamel caused two trenches to be made so as to in- 

 tersect 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 fiCsh vegetable 

 matter. This was covered, eighteen inches deep, with light 

 and poor loam, and upon the bed thus formed, seeds of the 

 common carrot (Daucus caro^u) and parsnip {Pastivaca sa- 

 liva) were sowed. The plants grew feebly till near the 

 end of the summer, when they assumed a very luxuriant 

 growth, grew rapidly till late in the autumn, and till their 

 leaves were injured bv frost. The roots were then ex- 

 amined, and were found of an extraordinary length, and in 

 form almost perfectly cyhndrical, having scarcely emitted 

 any lateral fibrous roots into the poor soil, whilst the rich 

 mould beneath was filled with them. 



In another experiment of the same season, the preceding 

 process was reversed, the rich soil being placed upon the 

 curface, and the poor beneath. The plants here grew very 



• Smith's Introdiiciion to Botany. 



D d 3 luxuriantly, 



