198 EXPERIMENTAL EVOLUTION LECT. 



growth of animals or plants, and it may be well to 

 dwell upon this. As a general fact, growth and 

 dimensions are correlated with the quantity and 

 quality of food. All breeders know what is the most 

 suitable food for their animals, according to the result 

 they wish to obtain ; all agriculturists know exactly 

 what are the manures they must use, according to 

 the soil on which they grow their plants, and the 

 species, the varieties even, that they put under culti- 

 vation. These facts have been put beyond doubt by 

 the numerous experiments which have been performed 

 in the English, French, and German agricultural 

 stations, and all have seen illustrations showing the 

 influence of the principal manures, if not the plants 

 themselves. Although these sorts of experiments 

 originated over a century ago although Tillet began 

 in 1770 to perform investigations with artificial soils 

 made with different proportions of natural earth, with 

 the view of ascertaining the influence of the com- 

 ponents on the crop obtained, the study of manures, 

 conducted in a scientific manner, has been only during 

 the present century made to yield the precise and 

 valuable results we are all acquainted with. 1 But 



1 Tillet 's experiments were published under the following title : 

 Experiences et Observations sur la Wgttation du Bit dans chacune des 

 Matieres simples dont les terres labourables sont ordinairement composes, 

 et dans different* melanges de ces matib-es, par lesquels on s'est rap- 

 procht de ceux qui constituent ces mtmes terres a labour. Histoire et 



