896 THE ZOOLOGIST. 
such as the blue, which are allowed to pass through. ‘‘ The rays 
on the further side of the red, not perceptible to our eyes—the 
so-called dark heat-rays—are likewise absorbed in their passage 
through the water, and an object at some depth under water 
would therefore only be reached by rays of high refrangibility, par- 
ticularly blue rays. The conditions of illumination for plants 
growing in the depths of the ocean are consequently in reality 
quite unfavourable. It is not only that a portion of the light 
falling on the surface of the water is reflected, and the other 
portion is weakened by its passage through the water, but besides, 
those rays which are necessary to the formation of organic matter 
by the chlorophyll granules in the plant-cells are abstracted from 
the light which passes through; for the chlorophyll granules 
need just the red, yellow, and orange rays if they are to perform 
their functions; only under the influence of these rays can the 
decomposition of carbonic acid, the separation of oxygen, and the 
formation of carbohydrates take place. The blue rays do not 
assist at all in this respect ; they are even hurtful to these pro- 
cesses, since they assist the oxidation—that is, the decomposition 
of organic substance. Consequently, phycoérythrin, the red pig- 
ment of the Floride, now appears, and indeed so abundantly, that 
the chlorophyll granules in the interior are quite hidden by it. 
This colouring matter displays a very marked fluorescence, that 
is to say, it absorbs a large portion of the light rays falling on it, 
and gives out other rays of greater wave-length. The blue rays 
are to some extent changed by it to yellow, orange, and red, and 
thus the chlorophyll granules finally receive those rays which act 
as the propelling force in the decomposition of carbonic acid. 
But this also affords an explanation of the remarkable phenomenon 
that sea-plants are only coloured green close to the shore, and 
only in the most superficial layers of water, while lower down they 
appear red. Only quite on the surface the emerald-like Ulvacee 
and Hntermorphas sway hither and thither, forming thus a light 
green belt; these alge are to be sought for in vain in the depths 
beneath. Of the plants which flourish below this region it can 
no longer be said that they grow green; this mark of vegetation 
has entirely vanished. Green has given place to red. All the 
innumerable Floride are reddened—sometimes a delicate car- 
mine, sometimes a deep purple; then again a light brownish red, 
