ae 
Important New Theories in Agricultural Science. 169. 
that the chief source of supply is the atmosphere. This.ds an inter- 
esting point, which further research will verify. Schleiden shews 
the process to be eminently simple. He says in his work: Accord- 
ing to Link, Schwartz, and others, an acre of water meadow con- 
tains 4400 pounds of hay ; which, when dry, contains 45°8-per cent. 
of carbon. The hay then yields 2000 pounds of carbon, to which 
1000 pounds may be added in the portion of the year in which the 
grass is not cut, and the roots. To produce these 3000 pounds of 
earbon, 10,980 pounds of carbonic acid is requisite, which may be 
raised to 12,000 pounds to compensate for the nightly expiration. 
Now, Schubler has shewn, that an acre of so wretched a grass as 
Poa annua, exhales in 120 days (too low a computation) of active 
vegetation, 6,000,000 pounds of water. To supply the exigencies 
of the “egrin therefore, it is only necessary for the meadow to im- 
bibe 35 grains of carbonic acid with every pound of water. 
Mr Biteirss has-found also, that in a plant of any one of our ordi- 
nary crops, more than 200 grains of water must pass through it for 
a single grain of solid substance to accumulate within it. He states 
the evaporation from an acre of wheat, during the period of its 
growth, to be 114,860 gallons, or 73,510,000 gallons per square 
mile. With clover it is rather more; with peas and barley less. 
When we apply these calculations to a county or a kingdom, we are 
lost in the magnitude of the processes by which nature works, but 
we see the more clearly that on such a scale the quantity of mate- 
rial supplied by the air, though minute to the individual, becomes 
vast in the aggregate. We see, moreover, the necessity in under- 
standing the relations between the evaporation and rate of growth, 
ard the laws and effects of absorption in soils. A thousand pounds 
‘of dry calcareous sand will gain two pounds in weight in twelve hours, 
when the air is moist, while pure agricultural clay will gain thirty- 
seven pounds. 
The source of nitrogen comes next to be considered: and this 
also is seen to be independent of manures. Hereupon it is observed, 
that ‘our domestic plants do not require a greater supply than in 
a state of nature. A water meadow which has never received any 
dung yields from forty to fifty pounds of nitrogen, while the best 
ploughed land yields only about thirty-one pounds, The plants for 
which most dung is used, as potatoes and turnips, are in fact propor- 
tionally the poorest in nitrogen.” That there is a supply indepen- 
dent ofthe soil, is further seen in the millions of hides furnished 
every year by the cattle of the Pampas, without any diminution of 
produce; and in the great quantity of nitrogenous matters, hay, 
butter, and cheese, carried off from pasture land, far more than is 
returned by the animals fed thereon. Experiments with various 
kinds of plants, on various soils, have satisfactorily demonstrated that 
inerease of nitrogen in the land and in the crop, does take place 
quite irrespective of supplies of manure. 
