Changes caused on the Spectrum, &e. By T. Palmer. 227 
but when treated with sulphuric acid it is either not changed or 
else carbonized. 
With regard to the second point or the colouring matter of 
plants, the green colour, which forms the most extensive class, has 
been treated upon in our primary consideration on chlorophyll; the 
red and yellow colours, as assumed by the leaves in autumn, are due 
to a chemical metamorphosis of the chlorophyll, and consequently 
the discoloration of the cellular tissue: see also Mr. Sorby’s paper 
“On the Various Tints of Autumnal Foliage.”* But independent 
of all this, there are the colours of the red cabbage, copper beech, 
and similar plants, all of which depend upon the existence of a 
special colouring liquid in the usually colourless epidermal cells, 
obscuring the chlorophyll which lies beneath. The bright colours 
of plants, and other parts of the inflorescence, as also on the lower 
surface of many leaves, Begonix Victoriz, for instance, as well as 
numerous herbaceous shoots, arise from the presence of matters of a 
different kind, almost always dissolved in the watery cell-sap. The 
colour of petals is ordinarily found to depend upon a certain 
number of the cells subjacent to the epidermal layer being filled 
with a coloured fluid, and the depth of the colour is proportionate 
to the number of superimposed layers of such cells, which act like 
so many layers of a pigment: each cell is usually filled with one 
colour when fully developed, but adjacent cells are often seen in 
variegated petals to contain distinct colours, the line of demarcation 
being accurately fixed by the cell-walls, through which the colours 
do not transude unless injured by pressure. In young tissues the 
colour has often a granular appearance in the cells, but this is a 
deception, arising from the mode in which it is developed. The 
colourless protoplasm, originally filling the cells, becomes excavated 
as it were by water bubbles, and the watery contents of the 
excavations become coloured ; they gradually enlarge, as the proto- 
plasm applies itself more completely to the walls of the cell, until 
they become confluent, and the coloared liquid fills the whole cell- 
cavity. ‘The isolation of the coloured juice in each particular cell 
seems to depend upon the primordial utricle, or parietal layer of 
protoplasm ; when this is injured by pressure or other external 
causes, endosmose is set up, and the integrity of the cell destroyed. 
In some cases the liquid colouring matter of flowers has been 
found to contain solid corpuscles; the red-colour cells of Salvia 
splendens and the blue ones of Strelitzia regina contain globules, 
and according to Von Mohl this is still more commonly the case 
with the yellow colours. In the yellow, perigonal leaves of 
Strelitzia regina, the colour is said to depend on the presence of 
crescentic filaments, floating in the cell-sap ; the white patches also 
on variegated and spotted leaves, such as those of Aucuba, Holly, 
* “Quart. Journal Se.’ vol. i. p. 64. 9 
8 
