for the purpose of discovering the true combination 
and attraction of the constituents of their colouring 
matter. He observed that oil received a green from 
plants by infusion, but not a perfect blue, neither 
would spirit of wine ; but water received all colours 
excepting a perfect green. 
The theory of Grew was built on the supposition 
that there exists a set of vessels, or as he terms them. 
Lymph aeducts, that abound in a compound of sul- 
phur and acid, which is favourable to the production 
of blues, reds, and purples; whilst another set, 
which he terms air vessels, contain a sub-alkaline 
salt, that mixes with the essential oil of the vegetable, 
and produces a green colour. The predominance 
of the Lymphaeducts, charged with their own com- 
pound, in various proportions, or in various com- 
binations with the air vessels, gives, he argues, all 
the beautiful variety of colours exhibited in the 
vegetable creation. 
The production of the different colours in vege- 
tables, by the predominance of acids or alkalies, we 
have found to be prettily shown by the following 
experiment. 
Make an infusion, by pouring hot water on the 
dried petals of red roses (rosa centifolia,) usually 
kept by druggists ; it will have but little colour till 
a small quantity of liquor potassae be added, when 
the infusion will become perfectly green ; add sul- 
phuric acid, and it will become red; and the colour 
may be alternately changed by the predominance of 
the acid or alkali. If the infusion be made of alcohol, 
in lieu of water, it will at first be colourless, but the 
ultimate results will be the same. 
Hort. Kew. 2, v. 3, 417. 
