Seaweeds and Leaf-green 
by Dr. Jénnson in Christiania harbour. He let down 
into the sea specially built glass boxes in which were 
certain living mosses. The constitution of the air in the 
chambers was exactly known, so that by testing the 
amount of carbonic acid and oxygen in the chamber 
after it had been left submerged for some time at dif- 
ferent levels, it was possible to know what the mosses 
had been doing. 
The results were very interesting, for it was found that 
the deeper the level at which the moss was placed the 
less carbonic acid was assimilated, and at a depth of 
sixty or seventy feet it was unable to do any work at all. 
This is just about the lower limit of algz in Christiania 
harbour. The water had absorbed all the assimilation 
rays at this level. 
If one could rest comfortably at the depths where 
the red alge live, and look up towards the sky, the 
whole world would appear blue. By their red colour 
these algze are able to use the blue rays of light, which 
are suspected to have some injurious effect on the 
physiology of plants unless so shaded. 
In the territory of Fucus and the other wracks and 
tangles the conditions are mixed. Some of the red 
rays are absorbed at high tide, whilst at low tide the full 
power of the sunlight beats down upon the chlorophyll, 
so that we find here a mixed condition. Mixed red and 
green do not make the Fucus brown, but the colouring 
matter will act as a protective mixture of some kind. 
So it follows that these colours of the seaweeds, 
although pretty and ornamental, are by no means acci- 
dental, but of very real use to the plants concerned.® 
Another step has been gained by Dr. Gaidukov’s ex- 
periments with one of the blue-green alge. This form 
(Oscillatoria sp.) shows great variations in its natural 
colour when found growing under different conditions. 
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