to the Earthy Constituents presented to their Absorbing Surfaces. 257 
tion of the phosphate which had escaped the previous action of the acid. 
These were not distinguished with any precision one from the other, because 
my object was merely to show that a large increase in earthy matter had 
resulted from the process of vegetation; but the several portions were all 
minutely examined for strontian, of which they furnished no trace. 
The same year I endeavoured to ascertain how much of this increase might 
be attributable to the rain, and the matters brought with it, by the following 
experiment : 
I procured six oblong boxes, of nearly equal size, coated internally with 
sheet zinc, two of which were filled with sulphate of strontian, two with pow- 
dered Carrara marble, and two with sea-sand, well washed both with water 
and muriatic acid. Of these, one of each kind was placed in a greenhouse, 
where they were protected from dust and rain; and the same number in an 
open garden, where they were exposed to both*. There was also placed in 
the garden a fourth box, of twice the dimensions, filled only with common 
mould. In each of the six smaller boxes were sown 780 grains of the seeds of 
the winged-pea trefoil (Lotus tetragonolobus), in the largest one double that 
quantity; and when the plants had severally grown up in their respective 
situations, they were cut down, dried, reduced to ashes, and examined, a com- 
parative analysis being at the same time made of a quantity of the seeds equal 
to that planted in each of the six smaller boxes. 
It will be seen from the following tabular view of the results obtained, that 
in every one of these cases there was an excess of earthy salt beyond that 
existing in the seeds, and in one case an excess of alkaline; those even which 
had vegetated in a soil chiefly consisting of sulphate of strontian obtaining, 
nevertheless, an increase of earthy matter, and this containing not even a trace 
of strontites, but consisting wholly of lime. In other respects the quantity of 
earth obtained appeared to keep pace with that in which the plant was supplied 
with it from without. Thus, the largest amount of lime was from the plants 
that had grown in Carrara marble, and of silex from those that had grown 
in sand. On the other hand, the great increase of calcareous salts in the pro- 
duce of the seeds that had grown up in the garden, in a soil consisting of sul- 
* [ am indebted to Professor Buckland for the use of a garden, in which the boxes were placed 
during the time the experiment lasted. 
