PROCESS OF VEGETATIOl^ 73 



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

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

 the ground in old established botanic o;ardens be duii 

 much deeper than ordinary, it frequently happens that 

 species wliich have been long lost are recovered, from 

 their seeds bein^ latent in the soil, as I have been assm'ed 

 by ^h. Fairbairn of Chelsea garden, and others. 



The integuments of the seed, having fulfilled their 

 destined oflice of protection, burst and decay. The 

 young root is the first part of the infant plant tliat 

 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, Faci, Ulvce 

 and ConJ'ervce^ it seems chietiy to an.swer the latter 

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

 the original root lasts only till the stems have esta- 

 blished themselves on some vegetable, on whose juices 

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

 withers away. 



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

 bud in a contrary direction, are ingeniously explained 

 by Dr. Darwin, Phi/tologia, 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 niost excited. This is perhaps more satisfactory than 

 any mechanical hypothesis. In whatever position seeds 

 happen to lie in the earth, the root n)akes more or less 

 of a curve in order to shoot downwards. Mr. Hunter 

 sowed a number of seeds in a basket of earth placed 



