Seaweeds and Leaf-green 



cellulose is burnt up. Carbonic acid gas, steam (water), 

 as well as light and heat reappear. 



But for such a fire a supply of oxygen is essential. 

 So when the sugar is formed in nature, which is the 

 reverse process, we find radiant energy, carbonic acid 

 and water being used up, but we also find that surplus 

 oxygen is given off. 



All green plants possess this power of forming new 

 organic material out of inorganic carbonic acid and 

 water, but there are certain interesting differences 

 between them. 



The first and lowliest group of plants, the seaweeds 

 or algae, are not all green. 



It has long been noticed that on an ordinary rocky, 

 gently sloping seashore where seaweeds flourish, there 

 are green, brown, and red kinds. 



Close to the level of high tide one finds bright, grass- 

 green enteromorphas and ulvas. The territory of the 

 slimy wracks and tangles or kelp, which are mostly of 

 an olive or reddish brown, lies between high and low 

 water-mark. 



At about the lowest level of the tide and below it to a 

 considerable depth, one finds neither green nor brown 

 algae, but only those graceful and delicate red, pink, or 

 purplish-red forms which are the ones usually selected 

 for preserving on blotting-paper. At a certain depth 

 one finds no living algae of any kind. 



No one could help speculating upon these colour 

 changes, and to-day we are almost in sight of a complete 

 explanation. 



The deep blue colour of the ocean is connected with 

 the fact that other colours in the sunlight, and especially 

 those red-yellow rays, which are the most important for 

 plant-life on land, are absorbed by comparatively shallow 

 depths of sea-water. This point was ingeniously tested 



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