THE SOURCES. OF THE NITROGEN OF VEGETATION, ETC. 461 
almost identically the same amount of Nitrogen as was provided in the seed and nitrate. 
Those in the other pot were allowed to go to seed, and 119 grains were formed. In this 
case, again, the Nitrogen in the produce was much more than had been supplied, and 
very much more when the residual Nitrogen in the soil and pot was taken into the 
calculation. Lastly, on this head, two pots of Wheat (also in 1856) were sown without 
nitrate, and two with 0:792 gramme of nitrate to each. There was a considerable gain 
of Nitrogen in each of the four cases. The actual amount of gain was greater in the 
cases where the nitrate was employed; but the proportion gained, to that supplied, 
was greater where no nitrate was used. 
To show the comparative efficacy of Nitrogen supplied in different conditions of 
combination, the following experiments were made during the season of 1856. 
Two pots of Colzas received, each 0:5 gramme of nitrate of potash; and two other 
pots of Colzas received each an amount of sal-ammoniac equivalent in Nitrogen to the 
0°5 gramme of nitrate. The two experiments with Nitrate gave equal amounts of 
Nitrogen inthe produce; and the two with sal-ammoniac, also equal amounts. But the 
two with nitrate gave more than 13 time as much Nitrogen in the produce, as the two 
with sal-ammoniac. In two other experiments, double the quantity of nitrate and 
sal-ammoniac, respectively, was employed, and the growth was allowed to extend over a 
longer period. The amount of Nitrogen in the produce was,‘in both these cases, very 
much greater in proportion to the amount supplied, than in the preceding experiments 
where the smaller amounts of nitrate and sal-eammoniac were used. It was, moreover, 
more than three times as much where the nitrate, as where the sal-ammoniac was 
employed. There was, too, where the nitrate was used, a considerable amount of 
Nitrogen assimilated beyond that provided, in the combined form, in the seed and 
manure. 
Experiments similar to the above were made with Wheat. Two pots, to each of which 
nitrate of potash was added, containing 0:110 gramme of Nitrogen, yielded, respectively, 
in produce, 0:218 and 0:224 gramme of Nitrogen. Two pots of Wheat, each manured 
with sal-ammoniac, containing also 0:110 gramme of Nitrogen, gave, respectively, in the 
produce, 0°161 and 0°124 gramme of Nitrogen. In the same way, nitrate of ammonia 
containing 0-110 gramme of Nitrogen gave 0:118 and 0:149 gramme, and phosphate 
of ammonia 0-116 and 0-150 gramme of Nitrogen in the matured Wheat plants. 
In regard to the experiments of M. VILLE referred to in this Division (8), he remarks, 
that the point at which the artificially supplied Nitrogen becomes exhausted is indi- 
cated by a lightening of the colour of the leaves, and that it is then that the plants 
begin to assimilate the uncombined. Nitrogen of the atmosphere. To secure this assi- 
milation, he considers that itis not only necessary that the supply of combined Nitrogen, 
and the vigour of growth, should reach beyond a certain limit, but that the artificial 
supply itself should, on the other hand, not exceed a certain limit. Further, the gain 
of Nitrogen in the experiments conducted on the plan now under consideration was so 
great, that, bearing in mind previously obtained results wherein the limit of the effect 
