373 DIRECTION OF THE GROWTH OF ROOTS. 



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

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

 common carrot (daucus carota) and parsnep (pastinaca ' 

 sativa) 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 by frost. The roots were then examined, 

 and were found of an extraordinary length, and in form 

 almost perfectly cylindrical, having scarcely emitted any 

 lateral fibrous roote into the poor soil, while the rich mould 

 beneath was filled with them. 

 ©thers in a rich Iq another experiment of the same season, the preceding 

 soil with a poor process was reversed, the rich soil being placed upon the 

 substratum. *^ ■ , rr.." , , 



surface, and the poor beneath. Ihe plants here grew very 



luxuriantly, and acquired a considerable size early in the 

 summer ; and when the roots were taken up in the autumn, 

 they were found to have assumed very different forms. The 

 greater part had divided into two or more unequal ramifi- 

 cations, very near the surface of the ground, and those 

 which were not thus divided tapered rapidly to a point at 

 the surface of the poor soil, into which few of their fibrous 

 roots had entered. 

 Plants growmg In other experiments seeds of almost all the common escu- 

 either "soil. ^^nt plants of a garden were so placed, that the young plants 



had an opportunity of selecting either rich or poor soil ; 

 ■which was disposed, in almost every possible way, within 

 their reach ; and I always found abundant fibrous roots in 

 the rich soil, and comparatively few in the poor. 

 Beans placed so The following experiment aftorded the most remarkable 

 to the air be- rcsult, and one the least favourable to the hypothesis, which 

 neath them and J have advanced in a former paper*, and to the conclusion 

 them! ^ which I shall now endeavour to support; and therefore I 



think it necessary to describe it very minutely. Some seeds 

 of the common bean (viciafaba), the plant with which 

 many former experiments were made, were placed upon the 

 surface of the mould in garden pots, in rows which were 

 about four inches distant from each other. A grate, formed 

 of slender bars of wood, was then adapted to the surface 



* Phil. Trans. 1806, page 1 : or Jourual, vol. xiv, p. 409. 



of 



