264 Dr. Dauseny on the Degree of Selection exercised by Plants, with regard 
admission. The latter supposition seems the more probable one, since, if we 
adopt the former, we ought to be able always to find traces of the earth dif- 
fused throughout the vegetable tissue; and I may relate an experiment of 
my own, which seems to confirm it, undertaken after the plan of those by 
means of which the ingenious M. Macaire of Geneva established his important 
doctrine with respect to the excretory function discharged by the roots of 
plants. 
A small Pelargonium was taken out of its pot, and its roots divided into 
two nearly equal bundles, one of which had its extremities immersed in a glass 
containing a weak solution of nitrate of strontian; the other, in one contain- 
ing pure distilled water. 
After a week had elapsed, the water contained in the aga glass was tested; 
but no strontian could be discovered in it, though a single grain in one pint of 
water would have been readily detected by my method. Hence it would 
seem that the strontian is not excreted by the roots. 
Yet this power of rejecting the earth in question, if possessed by the plant, 
must be held compatible with that of absorbing the water containing it, with 
which its roots are in contact. I took out of the ground a small Lilac (Syringa 
vulgaris), and introduced its roots into a glass globe containing seven pints of 
a weak solution of nitrate of strontian. In about a fortnight the quantity was 
reduced to three pints, the remainder having for the most part been absorbed 
by the roots; for evaporation was prevented by covering the surface of the 
water with a stratum of olive oil, and the mouth of the vessel with a cork. 
Unluckily, the original quantity of salt had not been estimated; but it was 
found that what remained in the water at the close of the experiment yielded 
69:4 grains of sulphate of strontian, equivalent to 39:2 of the earth. The four 
pints of water therefore consumed, if they had passed through the organs of 
the vegetable charged with their original quantity of nitrate of strontian, 
would have carried into its circulation 22:4 grains of this earth ; and as the 
water was absorbed at the average rate of about 44 ounces per diem, it fol- 
lows that more than a grain and a half would have been carried daily through 
the substance of the plant, supposing the salt to have been taken up in the 
same ratio as the water. Now on burning the plant, and examining its ashes, 
a trace of strontian certainly was detected, but its whole amount did not reach 
