520 
On the Food of Plants. 
Year. 
Niitme (if t'rop. 
Produce 
per 
Hectare. 
Dry 
Produce. 
Carbon. 
Hydro- 
gen. 
Oxygen. 
Nitro- 
gen. 
Salts , 
and 
Earths. 
1st. 
Potatoes 
12,800 
3,085 
1337M 
178-9 
1379-0 
46-3 
123-4 
S^Ull. 
Wheat . . . 
1,343 
1,148 
529 '3 
66-6 
498-2 
40-4 
27-5 
158-1 
310-2 
Straw of do. . 
3,052 
2,258 
1093'0 
119-7 
878-2 
9-0 
3 id. 
Clover, dried . 
5,100 
4,029 
1909-7 
201-5 
1623-0 
84 G 
■llh. 
Wheat . . . 
1,C59 
1,418 
653-8 
82-2 
615-4 
32*6 
34-0 
Straw of do. . 
3.7-0 
2,790 
ISaOM 
147-8 
1085-3 
11-2 
195-3 
Turnips 
9,550 
716 
307-2 
39-3 
302-9 
12-2 
54 4 
5th. 
Oats . . . 
1,344 
1,064 
639"5 
68-0 
390-5 
23-3 
42-6 
Straw of do. . 
1,800 
1,283 
G42-8 
69-3 
SOO-4 
O'l 
65-4 
Sum . . . 
Manui e used . 
40,418 
49,08G 
17,791 
10,161 
8383 • 1 
3637-6 
973-3 
426-8 
7172-9 
2621-5 
250-7 
2(13-2 
1010-9 
3271-9 
Dillpience . 
+7,630 
+4745-5 
+546-5 
+4551-4 
+47-5 
—2261-0 
The numbers express "kilogrammes" — the Ivilogramme is equal to 2-2 lbs. avoirdupois, very 
nearly. 
Tlie French land measure, the " liectare," is equal to 107,600 square feet, or 2-47 acres English. 
Now comes the question — is this nitrogen, thus taken up, the 
free nitrogen of the air, or is it derived from the trace of ammonia 
known to exist in the atmosphere? — The latter view is that 
adopted by Liebig", and certainly the evidence is in his favour. 
When azotized organic matter, an animal body for instance, un- 
dergoes putrefactive decomposition, it is known that the nitrogen 
is always disengaged, chiefly in the shape of ammonia : this is 
constantly the case, the hydrogen and nitrogen presented to each 
other in their nascent state by the breaking up of the organised 
body immediately unite. Carbonic acid is also a constant pro- 
duct of putrefaction, and neutralizes the ammonia produced, 
forming an extremely volatile salt, which rises in vapour into the 
atmosphere, and there accumulates until the first shower of rain 
brings it down in a state of solution. 
Ammonia is a substance exceedingly interesting in a chemical 
point of view, from the curious transformation which itself and its 
compoimds are capable of undergoing ; and it is easy to trace the 
peculiar facilities which this Protean nature gives for the pro- 
duction of the complicated azotized principles, such as gluten in 
the seeds of the grasses, the alkaloids in various medicinal plants, 
cScc. 
For plants growing in a state of nature this small but constant 
supply of nitrogen is amply sufficient ; but in those raised by 
artificial culture, especially when, as in the case of wheat and 
other grain, the whole plant, and more particulai'ly its azotized 
