WORTHY MODELS. 403 



they opened the way to a closer and more exact observation 

 than could have been had in their absence. 



An admirable model of experimental inquiry may be found 

 in Prof. Ville's " Six Lectures on Agriculture." The subject 

 is the " Nutrition of Plants." We know from accurate experi- 

 ment, that plants require for their growth a supply of cer- 

 tain substances or elements, which chemistry informs us of, 

 that stand to them in the relation of food. Now, the two 

 great questions which concern agriculture are : — 1st. What are 

 the food elements agricultural plants require? 2d. How can 

 these be applied to the nutrition of plants ? To answer these 

 questions, Prof. Ville instituted a series of experiments, so 

 simple in character, and yet so conclusive, as to command our 

 admiration. He says, " The soil could not be known with 

 accuracy, for chemical analysis had completely failed in ascer- 

 taining its composition. I resolved to substitute for it, an 

 artificial mixture, all the elements of which were clearly 

 defined. In this way, I arrived at producing vegetation, in 

 pots of china-biscuit, with calcined sand, and perfectly pure 

 chemical products." 



The weight the plants attained, in soils of known composi- 

 tion, differed much, clearly showing that one mixture was 

 more conducive to plant-growth, than a soil differently fur- 

 nished. Prof. Ville was not satisfied with a few experiments, 

 but made many, all with the idea of excluding from the plant 

 al! those elements of nutrition that were not designedly 

 furnished. The conclusion to which the experiment pointed 

 was verified afterwards on a larger scale, in actual field-cult- 

 ure. In this system of Prof. Ville, the plant analyzed the 

 soil, — its own appetite guiding its choice of food. The pro- 

 fessor had only to stand by, and observe what food the plant 

 preferred. By observation of the behavior of the plant in the 

 presence or absence of definite chemical agents, we are led to 

 the true principles of fertilization. 



In an inquiry directed to discover the influence of in-breed- 

 ing of plants, and of cross-breeding, as affecting their vigor of 

 growth, Darwin designed a series of experiments, which, to 

 quote his own words, " if they continue to give the same results 

 as hitherto, will forever settle the question of the good effects 

 of crossing two distinct plants of the same variety, and of the 



