PROCESS OF VEGF.TATIOX. 95 



Fuel, IjhcB and Conferva^ it seems merely 

 to answer the latter purpose. In the Dodder, 

 Cifscuta, a parasitical plant, the on<;inal root 

 lasts only till the stems have established them- 

 selves on some vegetable, on whose juices they 

 teed by means of otlier roots or fibres, and 

 then withers away. 



The descent of the root, and the ascent of 

 the leaf-bud in a contrarv direction, are ino-e- 

 niously explained by Dr. Darwin, Fhi/lologia 

 Sect. 9- 3, on the principle of "the former 

 being stimulated by moisture, and the latter 

 by air, whence each elongates itself where it 

 is most excited. This is perhaps more satis- 

 tkctory than any mechanical h^-pothesis. In 

 whatever position seeds happen to lie in the 

 earth, the root makes more or less of a curve 

 in order to shoot downwards. Mr. Hunter 

 sowed a number of seeds in a basket of earth 

 placed on an axis, by which their position was 

 a httle altered exery day. After the basket 

 had thus made two or tiiree circumvolutions, 

 the young roots were found to have formed 

 as many turns in attempting to attain their 

 natural perpendicular direction. J\Ir. Knight 

 has asccrlainctl, Phil, Ti-am^.fQr 1806', that 



