170 Important New Theories in Agricultural Science. 
With respect to ammonia, “ it appears that one-thirteenth of a 
grain in every pound of water is sufficient for the exigencies of vege- 
tation, and there is perhaps no spring water in the universe which 
contains so little.’ Then as to sulphur and phosphorus, which 
are also among the constituents of plants, the quantity needed in 
proportion to the time of vegetation is so small, that one 540,000th 
of a grain of sulphuretted hydrogen per cubic foot, diffused through the 
atmosphere to a height of 3000 feet is all that is required. 
The consideration that cereals would soon disappear from the north 
of Europe, if not cultivated, and perhaps from nearly the whole of 
this quarter of the globe, adds weight to the arguments in favour of 
enlightened attention to the inorganic constituents of plants. The 
point is to bring the soil into harmony with the conditions by which 
growth may best be promoted. Much depends on the nature of the 
soil ; the darkest coloured lands are generally the highest in tem- 
perature, hence the advantage of vegetable mould, while deep light 
sands and clay, which turn almost to stone in dry weather, weary 
- and vex the cultivator by their unprofitableness. It is to be re- 
membered, however, that soils which have the highest temperatures 
of their own, may not be those most susceptible of receiving heat,— 
that is from the sun, because some lands are warmed by the 
springs that irrigate them. Here we have an explanation of the 
phenomena of certain soils, which are warm in winter and cool in 
summer. ‘The application of humus evolves heat by the process 
of combustion, and sand, lime, clay, and humus, are the combinations 
needed, the clay being in a proportion of from forty to fifty per cent.; 
if less than ten per cent. the land will be too light and poor. 
Schleiden in summing up insists strongly on the necessity of 
selecting good seed; that from a barren soil, he observes, is likely 
to be more true to its kind than from well manured land, Also, 
that the time for sowing should be adapted to the acquirements of 
the plant, and it will surprise many to read that he advocates a 
less frequent use of the plough. He holds ploughing to be ‘a 
necessary evil, one to be employed only so far as necessity requires,’’ 
because of the too frequent loosening of the soil, the decomposition of 
humus is so rapid as to overbalance the benefit supposed to arise 
from exposure to the atmosphere. 
Such is a brief outline of some of the views of one who holds a 
high position among men of science ; and though in some particulars 
they may seem to be at variance with practice in this country, there 
is much in them worthy the attention of intelligent cultivators. 
An example to shew that the application of manure to fields might 
be more limited. 
A few years ago, the Rev. S. Smith, of Lois Weedin, in the 
neighbourhood of Banbury, instituted a course of experiments on 
this very point, and with results which are singularly interesting. 
He took a field of four acres, having a gravelly soil, with clay, 
