526 MB. J. B. LAWB8, DB. GILBERT, \M» DB. FUGH OH 



1( will be remembered that, under equal circuit tan© of (oil and season, l incus 



crops yield two, three, or more times :is much Nitrogen pet ■>< n I i uninaei ons ones. 

 Yet, whilst the latter are very characteristically benefited by the ose of direct nitro- 

 genous manures, the former, yielding so much more Nitrogen, are aot -<,. Again, the 

 Graminaceous crop, requiring for full produce such direct supply of available Nitrogen 

 within the soil, is very much increased, beyond what it would be if it succeeded a crop 

 of the same description, when it follows a Leguminous crop, in which has been carried 

 off so much Nitrogen. 



Experiments such as those now specially under consideration can obviously ; 

 upon a lr\\ only of the circumstances with which may be connected the causes of this 

 difference between the Graminaceous and the Leguminous crops. Without, therefore. 

 pretending adequately to discuss this wide subject, we will consider it only so far as our 

 immediate facts appear to hear upon it; they seem to limit us to the consideration of 

 the following cases: — 



1. The difference maybe due to the decomposition of nitrogenous compounds during 

 the growth of the Graminaceous plants, and to the evolution of free Nitrogen. 



2. The Leguminous plants may assimilate the free Nitrogen of the air. and thus, not 

 only allow the resources of the soil to accumulate, but also leave within it an additional 

 quantity, in roots and other vegetable debris, from that which has been assimilated, as 

 above supposed. 



3. It may be due to the operation of both these causes. 



So far as the facts we have already considered go, the difference in question cannot 

 be explained according to the first of the above suppositions; and others, to which we 

 shall have presently to refer, will be seen to afford confirmatory evidence on the point. 



With regard to the second supposed explanation, the results we have now to record 

 of our experiments with Leguminous plants are not of themselves sufficient to settle 

 every point which it involves. Reference to the Appendix will show that, in several 

 cases, we failed to get healthy growth with Leguminous plants. A doubt might hence 

 be raised, as to the value of those experiments in which we were successful under 

 circumstances so nearly identical with those of our failures that it was not easy to 

 account for the difference of result obtained. In those cases, however, in which we 

 have succeeded in getting Leguminous plants to grow pretty healthily for a consider- 

 able length of time, the results, so far as they go, confirm those obtained with 

 Graminacete, not showing in their case, any more than with the latter, an assimilation 

 of free Nitrogen. 



In 1857, we commenced several experiments with beans, but they grew well in 

 only one of the shades. These, however (especially one plant out of the two in the 

 same pot), progressed remarkably well for a period of 10 weeks, during which time the 

 amount of carbon was increased five-fold, more than three-fourths of the total Nitrogen 

 of the seed was appropriated, and the plants probably only ceased to grow when the 

 remainder of the latter became so distributed in the soil as not to be available to them. 



