702 The Sources of the Nitrogen of mir Legxmiinoiis Groups. 
some conditions. It has also been clearly shown, that due in- 
fection of the soil and of the plant is an essential to success. 
The evidence at the same time points to the conclusion that 
the soil may be duly infected for the growth of one description 
or some descriptions of plant, but not for some other descrip- 
tions. The field experiments on leguminous crops at Rotham- 
sted have further shown, that land which is, so to speak, quite 
exhausted so far as the growth of one leguminous crop is 
concerned, may still grow very luxuriant crops of another 
description of the same family, but of different habits of gi'owth, 
and especially of different character and range of roots. This 
result, though imdoubtedly more or less due to other causes 
also, is, nevertheless, in some cases doubtless dependent on the 
existence, the distribution, and the condition, of the appropriate 
microbes for the due infection of the different descriptions of 
plant. In fact, it is pretty certain that success in any system 
involving a more extended growth of leguminous crops in our 
rotations will not be attained without having recourse to a 
considerable variation in the description of leguminous plant 
grown. Another essential condition of success will pretty cer- 
tainly be the liberal application of potash and phosphatic 
manures for the leguminous crop. Then, the questions would 
arise — how long the leguminous crop should occupy the land ; 
to what extent it should be consumed on the land, or the manure 
from its consumption be returned ; or under what conditions 
the whole, or part, of it should be ploughed in? Lastly, it is 
probable that more benefit would accrue to the lighter and poorer 
than to the heavier or richer soils by any such extended growth 
of leguminous crops. 
J. B. L.vwEs. 
J. H. GiLliEKT. 
THE NITRIFYING FERMENTS OF THE SOIL. 
The salt, or chemical, known as nitrate of lime may, without 
hesitation, be described as the most important plant food con- 
tained in the soil. Imagine, if we can, a soil utterly destitute 
of it, incapable of forming it, and not supplied by manuring 
with any nitrogen-containing substance from which it can be 
formed. Such a soil, however kuid in texture, however well 
situated, drained, and tilled, however well supplied with the 
purely mineral ingredients of plant food, is not capable of 
growing the barest pretence of a crop of corn, roots, or -grass. 
Or consider the actual and very common case of two soils, good 
