THE VEGETABLE KINGDOM. 401 



require carbon and nitrogen. The grasses demand a cer- 

 tain quantity of silica. The stalk of the wheat-plant con- 

 tains a pretty large amount, but this substance strengthens 

 the powerful stem of the bamboo in a much more decided 

 manner. According to Davy, the latter contains as much 

 as seventy-one parts of silica in a hundred, and like our 

 flints strikes fire with the steel. According to De CandoUe, 

 analysis demonstrates that other vegetables absorb iron, 

 and even gold. Copper has also been found in coflTee and 

 wheat, and a chemist has computed that in France 3650 

 kilogrammes (8055 lbs. avoirdupois, omitting grains) of 

 this metal yearly enter into our food through the medium 

 of this cereal.^ 



Seeing the quantity of water that plants absorb every 

 day, Boyle concluded that this fluid was alone used for 

 their nutrition. The opinion of the celebrated English 

 philosopher was adopted by Van Helmont, and he thought 

 he had proved it to demonstration when he saw a Avillow 

 continue to flourish which he only watered with rain-water, 

 at that time considered to be wonderfully pure. 



Science has overthrown these views by proving that dis- 

 tilled water is in no way sufficient to support life in the 

 plant. 



The aerial organs of vegetable life also play a great part 



1 It ia now considered that the inorganic ingredients in plants are as absolutely 

 necessary to their existence as carbon and oxj'gen. In addition to such well- 

 known elements of tissue as silicon, chlorine, potassium, &c., modern research has 

 shown the presence of zinc, fluorine, ciBsium, rubidium, and manganese. The 

 ash of silk contains manganese derived from the mulberry-tree or other plant on 

 which the silk-worm has fed. Aluminium has been found in certain species of 

 Lycopodium and Selaginella, and zinc in the violet. CiBsium and rubidium have 

 been detected in tobacco and beet-root. Carbon sometimes exists to such an 

 extent that it constitutes half the weight of the dried plant. All food, however, 

 presented to the plant must be oxidized, or the plant cannot take it up. It is even 

 probable that all ammonia becomes oxidized before assimilation by the plant. — 

 Popular Science Reviev), vol. vii. p. 56. — Tr. 



