148 PRINCIPLES OF GARDENING. [CH. IV. 



to the water improves the green hue of her boiled 

 vegetables. That this is the cause of the pheno- 

 menon is testified by direct experiment. Blanched 

 celeiy and endive, and the -white inner leaves of the 

 cos-lettuce, contain about one-third more water than 

 the same parts when green ; and if submitted to 

 destructive distillation do not yield more than half 

 so much carbon. Then, again, if a plant of celerj- 

 is made to vegetate in the dark, under a receiver 

 containing atmospheric air, with the addition of not 

 more than one-twentyfifth part of its bulk of a mix- 

 ture of carburetted hydrogen, and hydrogen such as 

 is afforded by the distillation of coal, that plant, 

 though it becomes paler than when grown in the 

 daylight, still retains a verdant colour. 



So effectual is the metamorphosis of plants 

 effected by excluding them from the light, that Pro- 

 fessor Robinson brought up from a coal-mine, near 

 Glasgow, some whitish-looking plants of wliich no 

 one could detect the name or character. Aft^er 

 exposure to the light, the white leaves decayed, and 

 were succeeded by green ones, which speedily re- 

 vealed that the plants were tansy. They had found 

 their way into the mine in some sods from a neigh- 

 bouring garden ; but though they had retained life 

 in its dark galleries, they had entirely lost their 

 natural colour, odour, and combustibility. This is 

 only in accordance with the gardener s yearly expe- 



