THE VEGETABLE KINGDOM. 517 



The difference is well marked when we experiment with 

 seeds which germinate very quickly. One patch will be 

 covered with close green vegetation, while on the other 

 not a single plant has yet issued from the ground. 



Following Ingenhouz and Scnnebier, men have long 

 taught that light Avas opposed to germination. This is an 

 error, as Saussure noticed. Nevertheless all the coloured 

 I'ays of light are not ftivourablc to it; the chemical and the 

 calorific rays have each an opposite action upon this phe- 

 nomenon. The former, which are the blue and the violet 

 rays, clearly increase its activity; the latter, the red and 

 3'ellow rays, are hurtful to it.^ 



A knowledge of the fundamental conditions demanded 

 by vegetation explains certain phenomena which have 

 occasionally astonished the vulgar. When these conditions 

 are wanting, seeds are often preserved torpid for a long 

 time in the place Avhich incloses them, and then when they 

 find themselves under the influence of favourable circum- 

 stances, they cover a site with a form of vegetation m\- 

 known there Avithin the memory of man. 



Thus, according to the account of Eay, after the great 

 fire of London, the hedge-mustard {Sisj/mbrium Irio) all at 

 once grew thickly on the ruins of this city where previously 

 it was unknown. When certain forests are burned we see 

 plants spring from their soil Avhich were never previously 

 known there. Analogous facts have been noticed after old 

 marshes have been dried up. Their beds laid bare are 

 sometimes covered with an entirely new form of vegetation, 

 quite unknown in the country, and arising doubtless from 



1 With regard to the action of liglit, the Ijalance of eviJeuce seems to be in 

 favour of the opinion expressed by Mr. Hunt, which is very nnicli to the same 

 effect, viz. that the bkie rays promote germination, while tlie yellow light-giving 

 rays impede it. — Popular Science Review. — Tr. 



