53 2 Theory of the Nutrition [BOOK in. 



carbon dioxide of the atmosphere without the co-operation of 

 the humus, and that consequently the favourable effect of a 

 soil rich in humus on vegetation must be due to other causes 

 than those which were assumed by the humus-theory. We 

 cannot describe the further services rendered by Boussingault 

 to the theory of nutrition, for this would take us too much into 

 technical details, and the best and most important of his 

 results were first given to the world after 1860, and do not fall 

 therefore within the limits of this history. But it should 

 be mentioned that Boussingault must be considered the 

 founder of modern methods of conducting experiments in 

 vegetation. Liebig had before spoken in terms of sufficient 

 severity of the miserable way in which experiments on the sub- 

 ject of the nutrition of plants were managed after de Saussure's 

 time till later than 1830, but he did not himself introduce better 

 methods ; this was reserved for Boussingault. One instance 

 may be given ; those who desired to decide the question of 

 the humus by experiment, such as Hartig in conjunction with 

 Liebig and others, generally adopted the plan of supplying 

 plants with compounds of humus-acid, and seeing what 

 would be the result. Boussingault did as Columbus with the 

 egg ; he simply made plants supply themselves with food in a 

 soil artificially deprived of all trace of humus and containing a 

 mixture of food-material, in order to prove beyond question 

 that they do not need humus. 



In Germany also Prince Salm-Horstmar made similar experi- 

 ments to those of Boussingault ; he occupied himself chiefly in 

 determining the relative importance of the acids and bases of 

 the ash in the nutrition of plants, whether any and which of 

 them are indispensable ; these are questions which approached 

 their solution only after 1860, and some are not yet decided. 



The establishment of the facts, that plants containing chloro- 

 phyll derive the whole of their carbon from the carbon dioxide 

 of the atmosphere, and that the latter is also the original source 

 of the carbon in plants and animals which do not contain 



