122 
Transactions of the 
TMonthly MicroecopUal 
L Journal, Sept. 1, 1869. 
pointing the way to an interesting department of physical science, 
in which the microscopist equally with the chemist may reap a rich 
harvest. 
It is a generally received opinion that the chromnle of flowers 
is due to the chemical action, actinic rays, of light on the juices or 
protoplasm of the plant during growth. It is known, however, that 
the powerful action of light, in some instances, tends to decolorize 
flowers : therefore the gardener screens his choice tulip from the 
direct rays of the sun. It is evident that the phenomena associated 
with the formative colour process, which lends so much beauty to 
the floral world, is only half explained by the light hypothesis. 
Besides light, there must be other forces at work which enable the 
plant to separate from the soil, or select from within its tissues, 
certain constituents, of which we know little, such as those stored 
up in the woody material of the stem or root, yet so far removed 
from the presence of light that they appear associated with it only 
in a small degree. In such situations are found very large quan- 
tities of colouring matter, difl'ering in character to that of the 
petals; the stem or root, at first green, becomes brown, red, or 
black, and ultimately forming dye-woods, which are of so much im- 
portance in a commercial point of view. 
No doubt light is an indispensable agent in the production of 
the cromule of flowers ; and the curious part of the change is that it 
should be so diversified in the petals, imparting to them briUiancy 
and variety of the most perfect and pleasing character. The modifi- 
cations of tints are supposed, in a measure, to be owing to the nature 
of the cuticle through which the colour in the interior of the petals 
is viewed ; if the colour is more or less yellow it is modified by the 
character of the more superficial cells. This, however, ofiers no ex- 
planation of the colouring matter found in the roots, and which 
must difler in its nature with the chromogen of the petals. It is 
remarkable to notice that although certain plants, as the beetroot, 
readily yield up their colour to water, nevertheless during the state 
of health and vigour they seldom part with any considerable 
portion of it to the soil in which they grow, not even during long- 
continued rains. The alkanet, the root of which is the great 
storehouse of colour, will not, under any circumstance, part with 
it to water. Spirit, oil, and turpentine are its particular solvents. 
"Will not spectrum analysis enable us to solve some such mysteries 
in vegetable physiology, or explain the optical and physical differ- 
ences of two bodies growing on the same stem ? 
The colours of flowers, botanists tell us, may be arranged in two 
series, the zanthic or yellow, and the cyanic or blue, while red is 
common to both, and green intermediate. The red colour of 
certain leaves is owing, it is thought, to an excess of acid in their 
juices. This fact appears to receive support from the circumstance 
