526 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
It will be remembered that, under equal circumstances of soil and season, Leguminous 
crops yield two, three, or more times as much Nitrogen per acre as Graminaceous ones. 
Yet, whilst the latter are very characteristically benefited by the use of direct nitro- 
genous manures, the former, yielding so much more Nitrogen, are not so. 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 bear 
upon a few 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 bear upon it; they seem to limit us to the consideration of 
the following cases :— 
1. The difference may be 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 débris, 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 
Graminacez, 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. 
