130 
Transactions of the 
["Monthly Microscopical 
L Journal, Sept. 1, 1869. 
rather an exception to the rule, as rarely in my experiments did 
yellow solutions appear to be materially acted upon by alkalies. 
Yellow rose- petals form a deep amber or orange coloured solution, 
which is brought nearer the yellow by carbonate of soda. The 
addition of either a vegetable or mineral acid produces little or no 
change in the colour of the solution, nor do they cause any absorp- 
tion of the spectrum ; caustic potash and liquor calcis deepen the 
colour, changing the solution to a greenish-yellow, but no corre- 
sponding change takes place in the spectrum. The Brazil wood 
solutions produce the absorption reactions of the reds ; that is, both 
with its pink and red solutions there is an exaltation of the red ; a 
broad band in the green, which some tints seem to divide into two ; 
another in the blue, with a deepening of the blue and violet. 
The yellow tulip solution is quite as much unaffected by re- 
agents as that of the rose. From the tulip-petals a yellow crys- 
talline matter is obtained, which no doubt is identical in its character 
with Dr. Thudichum's Luteine, which he says " shows three absorp- 
tion bands in the blue violet and indigo portion of the spectrum, 
and are indicative of the presence of this body in yellow solutions." 
I have observed that in a very great many instances solutions 
obtained from either flowers, leaves, or stems of plants, produce 
uniform results on the spectrum. The evergreen berberries with 
their pretty leaves, some of which are a reddish- green or deep 
purple, and produce an abundance of orange-red flowers, all yield 
solutions to both water and spirit, which give a most interesting 
set of absorption bands, at least six in number ; the solutions keep 
well, and the spectrum is very permanent. The highly-extolled 
Peruvian Coca, the leaves of which are said to sustain the life of 
the aboriginal races for a long time, chiefly derive their nutritive 
powers from the large quantity of saccharine matter contained in 
them ; from its flower or leaf a fine bright-green is extracted by 
either water or spirit, producing a sharply-defined set of absorption 
bands nearly resembhng the berberry. I find that numerous dif- 
ferent solutions yield an almost identical series of absorption bands, 
as the pine-apple, digitalis, hyoscyamus, senna, belladonna, lau- 
restinus, buckthorn, &c. With Professor Stokes, I believe that 
spectroscopic examination of the constituents of plants and animals 
will certainly aid in their identification, " the force of the addi- 
tional evidence being greater or less, according as their optical 
characters are more or less marked ; or it will establish a difference 
between substances which might otherwise erroneously have been 
supposed to be identical." 
The blue series of colours in flowers are exceedingly difficult to 
extract, they resist almost every solvent of other colours. I believe 
they have rarely been obtained in a pure form ; but if a small 
quantity of red enter into their composition, then the colour is 
