178 
GARDENING AS A SCIENCE, 
While perusing three different directions for effecting the desired change, we 
perceived that it was the object of two of the experimenters to introduce by the 
roots a quantity of some salt of iron into the organism of the Hydrangea. One 
writer directs pure black peat,"and to water occasionally with a solution of alum : 
another employs sandy yellow loam as the staple, blending with it a quantity of 
fresh sheep-droppings ; the third uses black heath mould, which he calls peat ; and 
subsequently waters with an aqueous solution of the same earth. Now, alum is 
a super acid, — sulphate of alumine, and potass ; and therefore, the excess of acid 
presumes the possibility of dissolving a portion of the iron contained in the black 
peat, while in the second case, the yellow loam is supposed to furnish an abundance 
of the oxide of iron. But heath-mould contains very little iron ; and as to the 
oxide of the loam, it exists in a condition not to be dissolved by water. 
There is fallacy therefore in all these modes of operation ; and if ever the tran- 
sition of colour have been effected thereby, it must be referred to the vegetable 
matter {humus) of the heath soil, and to the gradual conversion into humus of the 
sheep-manure combined with the loam. 
As a blue-flowering Hydrangea, though rarely seen, may be an object of 
interest with many amateurs, a very simple experiment may be tried, which, if it 
be not successful in its direct object, will assuredly produce a marked change in 
the character of the foliage. We saw such a plant, above ten years ago — the 
only one in the vicinity ; and since we commenced this article, had an opportunity to 
converse with the gardener who grew it : the process he thus described : — 
A very young plant — say a well-rooted cutting — is cleaned from every particle 
of earth, and transferred to a small pot containing black heath soil (he pointed to 
our own heap of earth from Bagshot) mixed with a portion, perhaps one fourth, of 
very old, decayed cow-dung. Its truss of blue flowers was, we were assured, 
produced by this process ; the plant, however, was given away, and removed to a 
distance, and he never possessed an Hydrangea since that time. 
The question of a blue Dahlia was agitated for years, and at length appears to 
be entirely abandoned. It is of little moment, because, if dependent upon soil, the 
change, when effected in any individual instance, could never be maintained in 
soils varying with every locality. But as blue is a primitive prismatic colour, and 
apparently connected in some mysterious way with magnetism, it might not be 
trifling to suggest that some modification of electricity, or electro-magnetism, 
would perhaps be found to influence the colouring principle of flowers. 
We are so profoundly ignorant of the nature of vegetable sap, that we are 
unable to apply any rational argument to its course or future functions. It has 
been fashionable of late years to ascribe absorbent powers to the leaves, and some 
experiments have been brought to bear upon the theory ; but it should be 
recollected that all such experiments have been performed within glass vessels, 
wherein a plant or portion of a plant has been exposed to light, to the energy of 
chemical gases, to — in a word — a number of agencies, natural and non-natural, 
