Atmospheric Nutrition of Plants. 
5*35 
tity is" sufficient for the requirements of plants. M.M. Binoau and 
Boussingault pursued a very extensive scries of experiments bearing 
upon this matter, and from them it followed that whilst some plants 
may find a sufficient quantity of nitrogen in the shape of ammonia 
or nitric acid in the atmosphere to enable them to grow luxuriantly, 
others arc decidedly benefited if, in addition to the atmospheric am- 
monia or nitric acid, they are supplied through the medium of the 
soil with either ammoniacal salts or nitrates, or organic matters pro- 
ducing, on gradual decomposition, either nitric acid or ammonia. 
It is generally admitted that cereal crops arc more benefited by 
ammoniacal fertilizers than those commonly termed green crops. It 
is interesting to inquire as to the reason of this distinction. It would 
seem at first sight that green crops are more capable than cereals of 
assimilating atmospheric ammonia or nitric acid, because of the 
greater development of the leafy part. But it is only under certain 
conditions that root-crops can be thrown entirely upon atmospheric 
resources for their food. When plants like turnips grow rapidly, it 
generally happens that the soil contains a considerable quantity of 
organic matter, which favours the development of leaf; but when for 
some reason or other a deficiency of organic matter occurs, as is often 
the case in sandy soils, ammoniacal matters are supplied with great 
utility even to root crops. There are, however, other instances in 
which those manures are entirely wasted. How necessary it is then 
that we should have precise and accurate observations upon these 
important matters, and that we should not be satisfied with general 
statements not unfrequently made by men who, though eminent for 
scientific research, are deficient in the qualifications of mind that 
would entitle them to become the guides of practical men ! Many 
theories are extremely beautiful, simple, or interesting to all who 
take an interest in the progress of farming, but, from want of suf- 
ficiently minute attention to details, the farmer in his application 
of them may be seriously misled. The sum and substance of my 
observations is, that whilst we know that under certain conditions 
which have as yet to be still more minutely examined, and for certain 
crops, we have a sufficient atmospheric supply of ammonia and nitric 
acid, there are other crops, and more especially cereals, which do not 
grow with sufficient rapidity to be remunerative without the addition 
of nitrogenous manures to the soil. 
Upon the great influence of water, whether in the shape of watery 
vapour, dew, or direct rain, as necessary food to plants, I need not 
dweU, but I pass on to another effect of the atmosphere on vegetation. 
The observations I have hitherto made all tend to show the 
direct influence which the atmosphere has in the nutrition of plants ; 
but there is another part which it plays in the growth of vege- 
tables, which, though it may be called the indirect one, is so great in 
its effect, that we may say positively that all soils which are not 
penetrated by air are unproductive, no matter how much food they may 
otherwise contain. Cases are constantly brought under my notice, of 
soils, sent for examination, which are characterised as unproductive, 
but turn out to contain an abundance of all the mineral constituents 
