544 
On the Food of Plants. 
cause of the enormous difference in composition found even in 
different specimens taken from the same mass. 
The mode in which this substance acts, and the nature of the 
food it furnishes to corn plants, must be obvious from a glance at 
its composition — it closely resembles in this respect that type of a 
1 good manure, putrefied urine, in the immense quantity of azotized 
( matter and phosphates which it contains ; and we can be at no 
loss to understand how it is that by the use of such a substance 
the barren plains of Peru may for the time become converted into 
fruitful fields.* 
Nitrates of Potash and Soda. — There are probably no sub- 
stances capable of being used as manures upon Avhich more expe- 
riments have within a recent period been made than upon these 
salts, and especially upon the last, as its price is not generally so 
high as that of the former, in consequence of the large supply, 
and partly, perhaps, from its uselessness in the manufacture of 
gunpowder. It is necessary to state, however, that hitherto no 
satisfactory general resvdt has been arrived at ; some experiments 
on various kinds of crops have been attended with the most 
marked success, while in others either no perceptible difference 
was produced, or still worse, the result was a failure. A number 
of such experiments are related in the second volume of the 
.Journal of the Society, but it is impossible to deduce from them 
any general conclusion. 
Among the most important communications is that of Mr. 
Hyett, from a statement it contains of a very remarkable circum- 
stance, which, if confirmed by future experiments, will place the 
advantage of this manure on a higher footing than that which 
* Two specimens of South Sea guano, subsequently examined by the 
author, gave the following results: — 
No. 1. Pale brown, soft, and highly offensive — 
Oxalate of ammonia, with trace of cai-bonate, undecomposecll qq-o 
uric acid, brown organic matter, and water . . . ) 
Earthy phosphates, with very little sandy matter . . . 29*2 
Alkaline phosphate and chloride, with little sulphate . . 4*6 
100-0 
No. 2. Darker in colour, less offensive, and evidently more advanced 
in decomposition : it contained no uric acid — 
Oxalate of ammonia with little carbonate, organic matter, andl ^^.q 
water .......... j 
Earthy phosphates, with little gritty matter . . . . 41'2 
Alkalme sulphates, chlorides, and phosphates (both potash and) j^.g 
soda, the latter most abundant) . . . . . .1 
100-0 
— {Proceedings of Chemical Society of London, vol. i. p. 3G.) ' 
