158 AGRICULTURAL BACTERIOLOGY. 



high condition. The exact method by which the legumes 

 may be alternated with other crops, the proper legume for 

 each soil, the frequency with which the leguminous plant must 

 be cultivated on the soil to keep up the store of nitrogen, all 

 of these questions must be worked out in practice as the 

 result of experience. The complete solution of the problem is 

 no easy matter, even after a possible method of solution has 

 been pointed out. But, theoretically at least, it would seem 

 that there is nothing to prevent the agriculturist, after he has 

 sufficiently experimented in the various soils, from keeping his 

 store of nitrogen at a tolerably constant quantity. He need 

 not, in the future, be at the mercy of commercial fertilizers for 

 the purpose of furnishing his plants with this highly important 

 and necessary food. 



As an example of the practical utility of this method of im- 

 proving the yield of soil, may be mentioned a single experi- 

 ment. Half an acre of land was sown with alfalfa and the 

 next year with wheat. Besides yielding a valuable crop of 

 alfalfa the first year, the soil was so much improved that, when 

 sown with wheat the second year, it yielded $16 worth more of 

 wheat than a similar half acre which had not previously been 

 sown with alfalfa. 



NITROGEN FIXATION BY OTHER PLANTS. 



A final question arises, whether there are any other plants, 

 besides the great family of legumes, that are capable of acting, 

 cither alone or with bacteria, and fixing nitrogen. Our knowl- 

 edge in regard to this subject is as yet very incomplete. Some 

 experimenters, as stated above, have insisted that the property 

 of fixing atmospheric nitrogen is quite general among plants. 

 It has been claimed to exist in wheat, oats, mustards and a 

 variety of other plants including various algae. The claim 

 has been advanced that the property is a general one, and that 

 the legumes only differ from other plants in that their power 



