J. H. Oilhert—PoinU in connection witli -Vegetation. 187 



little doubt that it would do so. On the other hand, a good 

 crop of clover would appear to be attainable in soil comparatively 

 poor in nitrogen in its upper layers, and comparatively poor in 

 organic matter also; for, in the experiments already referred to 

 in which barley was grown after barley and after clover, the 

 large amount of clover obtained, and nitrogen assimilated in it, 

 was after six corn crops grown by artificial manure alone ; con- 

 ditions under which the amount, both of available nitrogen, and 

 of organic matter, in the upper layers of the soil, would be sup- 

 posed to be comparatively small. 



The answer of Deherain would probably be, that under the 

 circumstances supposed, the nitrogen would be in a condition 

 ef combination not 1 ition by the Gramineas; 



that, in fact, the ammonia formed would combine with organic 

 acids in the soil, jriel able as food 



for the Leguminosse. An objection to this view is, that if the 

 accumulation in the soil by time, of nitrogen in a condition 

 specially favorable for the ' Leguminosse were such as is here 

 assumed, we should expect the amount of nitrogen in the soil, 

 determinable by the soda-lime process, to be higher before than 

 after the growth of a leguminous crop ; whereas, on the contrary, 

 after the growth of a leguminous crop, the amount of nitrogen 

 so determinable in the upper layers of the soil is very apprecia- 

 bly increased. 



The evidence in favor of the supposition that the special 

 source of nitrogen to the Leguminosse is ammonia, or other 

 compounds than nitric acid, in the upper layers of the soil, is 

 then, to say the least, inconclusive. It remains to consider 

 whether it may not b< er in the soil or in the 



subsoil ? 



As already said, there is abundant evidence of the formation 

 and existence of a considerable amount of nitric acid in surface 

 soils; even in such as contain a rektiv< lj h - «">t of car- 



bonaceous and nitrogenous organic matter. For example, a 

 soil at Eothamsted which has been under garden cultivation, 

 and as such probably manured almost every year for centuries, 

 has successfully grown clover every war i.>r :,<: than twenty 

 years. This soil was shown by the late Dr. Pugh, and has 

 been again recently by Mr. Warington, to contain a consider- 

 able amount of nitric acid. But such .1 * al • 1 d, there is no 

 doubt, grow large crops of Graminese also ; which direct ex- 

 periments show to attain great luxuriance under the influence 

 of artificially : t ires. But such a rich garden soil 



contains an abundance of every thing— mineral constituents, 

 carbonaceous organic matter, and combined nitrogen in various 

 forms, and thus°the exact condit :<-s favor- 



able to the Leguminosse cannot at once be discriminated. 



