SCIENCE AS A FACTOR IN AGRICULTURE. 483 



the fundamental and unforeseen truth that the combination of 

 the elements under the form of organic compounds takes place 

 only in plants to the exclusion of animals, for which plants are ul- 

 timately destined to serve as food. The mysteries of the produc- 

 tion of useful plants and of the feeding of domestic animals have 

 been unveiled by it ; and these truths, so simple in our view, have 

 been fruitful in applications. 



Without enlarging upon a subject that would demand the most 

 ample development, it will suffice to recollect that the constituent 

 elements of plants have been divided into two groups : in one, such 

 substances as oxygen, the carbon of carbonic acid, the hydrogen 

 of water, and in a certain proportion the nitrogen of the air, are 

 borrowed from the atmosphere, which can furnish them in unlim- 

 ited quantities. Others, like the alkalies, lime, silica, iron, and a 

 part of the nitrogen, are drawn from the soil. Removed with the 

 crops, they should be restored to it, under penalty of a more or 

 less rapid exhaustion. Each plant requires special elements ; and 

 it is necessary in its cultivation to be assured that the soil already 

 has them, or to furnish them to it. Hence the long-disputed 

 utility of chemical fertilizers ; in them resides the whole secret of 

 the indefinite maintenance of the land and the entire art of inten- 

 sive cultivation. 



But, while mechanics is a useful auxiliary to agriculture, and 

 while the co-operation of chemistry is continually required, there 

 is another science of still higher importance, because it presides 

 over life itself in the animal as well as in the vegetable kingdom. 

 You have named it physiology. You all know to what extent a 

 knowledge of it is indispensable in order to define the conditions of 

 animal and vegetable production, and to assure the normal devel- 

 opment of living beings. You all know the importance of hygiene 

 in society for securing the health of men and then of animals, and 

 even of plants. Its function, long misconceived, is conspicuous 

 now in all eyes ; and it is one of the triumphs of science that it 

 has been able to prolong the duration of human life, to secure 

 immunity of our domestic animals against epidemics, and to ex- 

 tend its protection against the diseases which are destroying our 

 field products and are threatening the annihilation of agricul- 

 tural crops. 



But the preservation of the products is not all. We need also 

 to learn how to multiply productive beings ; and in this field, too, 

 science has, by the application of methods of selection, realized 

 most marvelous progress in agriculture. Not only has intensive 

 cultivation taught us how to draw a larger return than formerly 

 from a particular soil and a given surface, but by the selection of 

 seeds, we have doubled and tripled the formation of sugar in 

 beet roots ; by like selections, the production of the potato has 



