with many species of the tribe, to extend itself by climbing, is but im- 
perfectly displayed in our stoves, compared with the freedom of range 
which it enjoys in its own country. One species of Convolvulus an al- 
lied genus in the Caraccas was trained 5,000 feet in six months ; which 
shews the extraordinary activity of the vital principle, when stimulated, 
and ministered to, by = — i of scat: gece within the 
tropics. The chang of this and 
many other plants, is one of the most curious and interesting phoenome- 
na, effected by the chemistry of nature. However varied the hues or 
brilliant the colours of flowers may be, there is originally no difference 
between these parts and the most unadorned portion of the plant: “for 
such colours do not exist in their primitive state, but are communica- 
ted, as it were, to vegetation, by its own act. The tissue of plants is 
in itself completely colourless, of a silvery white (as may be seen in 
the pith of the elder, or petals of the white camellia), or of an exceed- 
ingly pale yellow; the matters contained in the cells, are with a few 
exceptions, of the same hue: but all is changed, when they are once 
exposed to solar light.” The sunlight enables them to decompose 
carbonic acid, and form a peculiar principle called chromule, which 
has the property of combining with variable quantities of oxygen. “ It 
is therefore probable that all the various colours of flowers with the 
exception of certain special cases, depend in general upon the various 
degrees of oxygenation of their chromule.” See more extended ob- 
servations on this subject translated from Decandolle, in Library of 
Useful Knowledge. Botany, p. 120. 
INTRODUCTION; WHERE GROWN; CuLTurE. The seeds were trans- 
mitted from Mexico about 1831, by Mr. Samuel Richardson (an offi- 
cer of the Anglo-Mexican Mining association) to'J. D. Powles, Esq. 
of Stamford Hill, by whom they were liberally distributed. The 
plant from which our drawing was made, flowered in the stove of 
Robert Barclay, Esq. of Layton, Essex; and we were obligingly sup- 
plied with specimens of the same variety of a more purple hue, by 
W. Taylor Copeland, Esq. M.P. of Layton. It requires the usual 
treatment of the stove species of Ipomea. Flowers in October. 
spe or THE NAMEs. 
Troma, from I7ro¢ C 1 and ¢ similar, from closely emer 
the genus siivolvnian patetdeechrr from ruber, red, and coeruleus, bl 
from the two hues of the flower at different periods of its expansion. 
SynonyMEs. 
Troma RUBRO-ca@RULEA, Hooker, in Botanical Magazine, folio 3297. 
