IN THE VEGETABLE KINGDOM. 185 



of hydrogen, as, for instance, the resins and fatty oils ; and there 

 occur some combinations of carburetted hydrogen which are 

 entirely free from oxygen, as, for instance, the ethereal oils and 

 caoutchouc. A decomposition of water may also be more readily 

 explained from a chemical point of view, than a reduction of the 

 carbonic acid; Alexander v. Humboldt has even observed a 

 development of hydrogen during the vegetation of several fungi. 



We possess very few reliable experiments from which we can 

 ascertain the relations under which plants generate organic matter 

 from water and carbonic acid during their exposure to the action 

 of the sun's light. According to certain observations of Saussure, 

 a plant of Vinca minor generated, under definite conditions, a 

 quantity of organic matter, in which there were contained 40*87$ 

 of carbon. In two plants of Mentha aquatica there was organic 

 matter produced which contained 50$ of carbon. 



The origin of the nitrogen in plants is a subject of far more 

 difficulty; for whilst carbonic acid and water are conveyed to 

 plants from almost every direction and under all conditions, we 

 are unable to detect the source from whence plants derive their 

 nitrogen. Both Saussure and Boussingault* have shown by the 

 most exact and ingenious experiments, that plants are unable to 

 condense free nitrogen from the atmosphere, and to elaborate it 

 into organic matter ; and they regard it as probable that nitrogen 

 passes into plants only in the form of soluble nitrogenous products 

 of decomposition of organic matter, and more especially in the 

 form of ammonia. Here again it is to Liebig that we are indebted 

 for the discovery of the hidden sources of this important element 

 of vegetable nutrition. Liebig has shown that the origin of the 

 nitrogen must be referred to the direct contact of ammoniacal 

 salts with plants, seeing that he found considerable quantities of 

 these salts in many vegetable juices. The juice of the maple, 

 the red beet, the birch, fresh tobacco-leaves, the tears of vines, 

 and all blossoms and fruits, contained a certain amount of 

 ammonia, without there being any indication that decomposition 

 had set in. Exact calculations show that far more nitrogen is 

 abstracted from well-cultivated fields than could have been con- 

 veyed to them by manure, or any other means. It has been seen 

 from experiments on the solid excrements of animals, that ordi- 

 nary solid animal dung, so far from containing much nitrogen, 

 often contains mere traces of it, and that such manure is entirely 

 inadequate to yield to plants the amount of nitrogen which is 

 * Ann. de China, et de Phys. T. 67, p 5, et T. HO, p. 353. 



