Seaweeds and Leaf-green 



by Dr. Jonnson in Christiania harbour. 4 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 algae 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 algae live, and look up towards the sky, the 

 whole world would appear blue. By their red colour 

 these algae 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. 5 



Another step has been gained by Dr. Gaidukov's ex- 

 periments with one of the blue-green algae. This form 

 (Oscillatoria sp.) shows great variations in its natural 

 colour when found growing under different conditions. 



32 



