76 
such, was very rare in Nature, and seemed to be injurious in excess, 
The blindness caused to the inhabitants of Alpine regions by the daz- 
zling whiteness of the snow, and the injurious effect of white-washed 
walls upon patients suffering from ophthalmia, were well known 
instances. We were, therefore, led to the conclusion that while white 
light, as a whole, was necessary to the human system, its division into 
coloured rays performed some part in the animal economy which could 
not safely be dispensed with, and this conviction was yet more forcibly 
impressed upon us, when we had to deal with the vegetable creation. 
That light was necessary to the growth of plants, we had abundant 
proof. Their respiration and consequent absorption of carbon were in 
direct proportion to the amount of light received, and ceased entirely 
during the hours of darkness, The slow and straggling growth of a 
potato in a dark cellar, and the change of properties caused by tying 
endive, or earthing up celery, were additional instances of the im- 
portant part which white light played in vegetable economy ; but it 
was with coloured light we had to deal at present. A careful examina- 
tion would probably prove that the proportions of different tints 
received by a plant amounted in the aggregate to white light ; but 
setting this aside as “‘ not proven,” it was remarked that the colour of 
a plant might be considered with reference to its distribution amongst 
various parts of that plant, and also with regard to its local surround- 
ings. 
A very cursory observation would show that different localities 
had their favourite floral colour ; nay, that whole countries manifested 
a predilection for some partlcular hue. It was probable that five 
sixths of the wild flowers growing in England were yellow, though the 
proportion was different at different times of the year, varying from 
blue in the cold spring (when the harebells, violets, and hyacinths 
bloomed) to red in the hot autumn, when every stubble field was 
covered with poppies, knapweed, pimpernel, and bartsia. But as we 
approached the colder regions of Scotland, Norway, and Lapland, blue 
flowers were far more frequent, while in the tropics we found every shade 
of red, from the delicate bloom of the cactus, growing under a forest 
shade, to the intense scarlet of ‘‘ Sturt’s Desert Pea,” found in the 
burning and exposed regions of central Australia. 
And now a natural law seemed to dawn through the apparent 
confusion. It was well-known that the heat of the solar rays was 
