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almost entirely concentrated in the red rays of the spectrum, diminish- 
ing in the orange and yellow, and almost or quite disappearing in the 
blue. Hence a surface which was intended to receive as much heat as 
possible should be constructed to absorb the whole of the red and 
yellow light, reflecting only the blue, like the plants of northern 
countries ; one intended to remain cold, even at high temperatures, 
should reflect the red, or red and yellow rays, as in the case of the 
gorgeous tropical plants; while those which, reflecting only yellow, 
absorbed a judicious mixture of warm red and cold blue, were 
eminently fitted for a temperature such as ours. It was then, by design, 
and not by chance, that the flowers of different climates were coloured in 
exact proportion to the amount of heat to which they were likely to be 
exposed, and, as he had already hinted, the rule held good with regard 
to the monthly succession of flowers. It would at once be observed 
-that there were numberless apparent exceptions to the rule thus 
broadly stated, but it would also be noticed that these exceptions were 
highly significant. The crouching violet, sheltered by hanging leaves 
from the sun’s rays, the wild hyacinth, growing beneath a thick and 
shady hedge, were virtually in a colder climate, and wore the Arctic 
garb of blue. The tall foxglove, standing perhaps six feet above the 
ground, the corn poppy, exposed to the full glare of an autumn sun, 
these had to endure heat, and must wear the livery of the tropics ; 
while the countless flowers of average height and average exposure 
‘were coloured with the characteristic yellow of our average 
climate. 
Another, and even more difficult subject must be noticed, the distri- 
tion of colour in the parts of an individual plant. We at once noticed 
that the stem, branches, and leaves—the circulatory and respiratory 
organs—were of a uniform green. This large absorbtion of red rays 
seemed to indicate that the circulation of sap, like that of blood, 
required a certain amount of heat for its maintenance, but we were at 
any rate safe in ascribing to the operation of these rays the decompo- 
sition of carbonic acid, which constituted the respiration of plants. 
The colours of the perianth had been, perhaps, sufficiently 
accounted for, but an item of some importance yet remained. 
He had hitherto spoken of light only with regard to its calorific 
qualities. It must not be forgotten that in the paler rays of the 
spectrum, but especially in the violet, there resided powerful chemica 
agencies, capable, as every photographer knew of decomposing the 
