146 



HUTCHINSON'S POPULAR BOTANY 



idea that as you descend deeper and deeper into the ocean, and the light 

 of day vanishes, a fiery yellow first succeeds, then a flaming red (the 

 "watery sea-hell" of Schleiden), then dark crimsons and purples, and 

 finally an impenetrable black, is partially, though not entirely, correct ; and 

 the circumstance has an important bearing on our present inquiry. Strictly 

 speaking, the colour of sea-water in reflected as well as in direct light, and 

 at all depths where the light can reach it is blue, a fact which is scien- 

 tifically accounted for by the high refrangibility of blue rays, which 



enables them to pass easily 

 through the water, while the 

 red, orange, and yellow rays, 

 which are far less refrangible, 

 are absorbed. Yet red and 

 yellow rays are absolutely 

 essential to plants contain- 

 ing chlorophyll if carbo- 

 hydrates are to be formed 

 and life and growth main- 

 tained * ; and the question 

 naturally arises, How do the 

 deep-sea Algce, which are 

 deprived of all but the blue 

 rays, compensate themselves 

 for this deprivation ? The 

 answer to the question affords 

 a striking instance of the 

 resourcefulness of ^Nature. 

 No marine plants inhabit 

 a deeper zone than the 

 Floridece or Eed Seaweeds, 

 and it is b}^ means of 

 the pigment which gives 

 them that colour that the 

 deficiency is remedied. This 

 pigment, which is known 



as phyco-erythrin (Greek phukos, seaweed ; eruthros, red), is fluorescent in a 

 high degree, and has the remarkable property of changing the blue rays 

 which visit the plant into yellow, orange, and red ones; so that the 

 chlorophyll granules contained in the underlying tissues are enabled to 

 carry on their functions in a regular manner, decomposing carbon dioxide 

 and forming organic substances just as do the green Algce which float 

 uptfn the surface of the water. In fact, the arrangement is quite as perfect 

 and efficient as is the lens arrangement in luminous Mosses. 



* The blue rays are said to be actually destructive of vegetable protoplasm. 



Photo by] [E. Step. 



FIG. 183. HONEY-COLOURED MUSHROOM. 



A couple of examples of this fungus from the group shown in fig. 

 182, but here photographed natural size. 



