PROCESS OF VEGETATION 73 



of Thistles, or of the Cress or Mustard kind, though 

 no seeds have been allowed to have access to it. If 

 the ground in old established botanic gardens be dug 

 much deeper than ordinary, it frequently happens that 

 species which have been long lost are recovered, from 

 their seeds being latent in the soil, as I have been assured 

 by Mr. Fairbairn of Chelsea garden, and others. 



The integuments of the seed, having fulfilled their 

 destined office of protection, burst and decay. The 

 young root is the first part of the infant plant that 

 comes forth, and by an unerring law of Nature it is 

 sent downwards, to seek out nourishment as well as to 

 fix the plant to the ground. In sea-weeds, Fuel, Ulvcc 

 and Conferva, it seems chiefly to answer the latter 

 purpose. In the Dodder, Cuscufa, a parasitical plant, 

 the original root lasts only till the stems have esta- 

 blished themselves on some vegetable, on whose juices 

 they feed by means of other roots or fibres, and then 

 withers awav. 



*/ 



The descent of the root, and the ascent of the leaf- 

 bud in a contrary direction, are ingeniously explained 

 by Dr. Darwin, Phytologia, sect. 9- 3, on the princi- 

 ple 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 satisfactory than 

 any mechanical hypothesis. 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 



