18 



SCIENCE. 



[N. S. Vol. XVII. No. 418. 



tion, nitrification, denitrification and fixa- 

 tion of free nitrogen. 



2. Those showing the fixation of free 

 nitrogen by microbes in symbiotic relation 

 to higher plants. 



The first group of observations including 

 the fixation of free nitrogen in the soil as 

 pointed out by Berthelot and others is of 

 great importance to agriculture, but the 

 amount of available nitrogenous plant food 

 produced by the various processes dis- 

 covered is not sufficient for the demands 

 of intensive farming. The truth of this 

 statement can be inferred from the fact 

 that, in addition to the enormous amount 

 of nitrogenous material obtained from 

 domestic and industrial sources, as well as 

 from the extensive deposits of guano, there 

 are, at the present time, about one million 

 tons of Chili saltpeter employed annually 

 by farmers the world over to maintain 

 partially the fertility of their fields. 

 : The second group of observations are of 

 greater interest to agriculture, since they 

 point out the way of securing from the 

 free nitrogen of the air an ample amount 

 of combined nitrogen to meet all the re- 

 quirements of intensive farming. They 

 make the farmer independent of the nat- 

 ural deposits of nitrogenous fertilizers, 

 and furnish him the means of preventing 

 his helplessness, in case these sources of 

 plant food should become exhausted or 

 otherwise unavailable. 



Prom the time of the ancients down to 

 the present day the legumes, especially the 

 clovers, have occupied a unique position 

 among agricultural crops. The beneficial 

 effects of a crop of clover upon subsequent 

 ■grain crops was a matter of practical ex- 

 perience in ancient and medisval times, 

 and this empirical knowledge was applied 

 more or less in the practice of agriculture 

 during those periods, as well as in modern 

 times. When the science of chemistry be- 



gan to shed light upon the production of 

 vegetable matter, and showed the relation 

 which plants, soil and air bore to each 

 other, and especially that certain elements 

 contained in the soil and air were essential 

 to vegetable growth, the peculiar properties 

 of the legumes received early attention. It 

 was soon learned that the leguminous 

 plants were preeminently nitrogen-gath- 

 erers. Having accepted the conclusions of 

 Boussingault in regard to free nitrogen as 

 true, the teachers of agricultural chemistry 

 were forced to explain this property of the 

 leguminous plants in various ways. Be- 

 sides the empirical observations, already 

 alluded to, many comparative experiments 

 were made which showed the beneficial 

 effects of legumes on subsequent grain 

 crops. As an example the experiment of 

 von Wulffen may be cited. One half of a 

 certain field was allowed to remain in bare 

 fallow, while the other half was sown to 

 yellow lupines. After the lupines had 

 fully developed the whole field was plowed 

 and sown to rye. The yield of the two 

 halves was determined separately with the 

 following results: 



Grain. Straw. 



After lupines 532.5 » 1,072 lb 



After bare fallow 322 lb 656.5 lb 



Here was a total increase in grain and 

 straw of 626 pounds on that half of the 

 field which had been sown to lupines, while 

 nothing from without had been added to 

 it except sixty pounds of lupine seed. The 

 results of this experiment also show, what 

 was claimed above, that the independent, 

 bacterial activity of the bare fallow fell 

 far short of producing sufScient available 

 plant food for a full crop of rye. 



In seeking an explanation for this effect 

 of the legumes, Boussingault determined 

 the amount of refuse, i. e., stubble and 

 roots, left in the soil by various crops. For 

 this purpose he had the roots, etc., collected 



