Seaweeds and Leaf-green 



sunlight falling on it and supplied with a continual 

 stream of sap by its parent tree. Under a microscope 

 one can see the small chlorophyll bodies, but the green 

 material forms only an inconceivably thin coating over 

 them. It may be one-io,oooth or even one-25,oooth 

 part of the thickness of a millimetre.* Supposing that 

 the light falling on the leaf of a lime tree during one 

 minute only is held up by this thin chlorophyll layer, 

 then the heat that would be produced in it might amount 

 to something like 6000° C. 



It is hardly likely that such temperatures are ever 

 realised, for the absorbed energy is probably spent as 

 rapidly as it is taken in. Water is being evaporated and 

 requires about 8 per cent, of the absorbed energy. 

 Another 3.3 per cent, is required for the chemical 

 cookery at work by which in the end sugar and starch 

 are produced in consequence of the splitting up and 

 rearrangement of carbonic acid and water. 



The details of the process are still very obscure or 

 rather form the subject-matter of a violent controversy. 

 Some authors hold that the green matter can produce 

 carbohydrates outside the living celly which would be 

 very interesting if true. Under strong light it may be 

 that chlorophyll is decomposed, and that one of the pro- 

 ducts is formaldehyde ; from this last substance sugar 

 might be formed without much chemical difficulty. 



But at any rate sugar and other carbohydrates are 

 formed in the leaves and subsequently worked up into 

 proteids and other food material of the living proto- 

 plasm. 



The process may be perhaps followed more clearly 

 if one reflects upon what happens when sugar or 



* That is, '000003937 of an inch or less. Compare Timiriaseff,^ Usher and 

 Priestley, 2 Ewart.^ Hydroxy! and nascent Hydrogen are supposed by others 

 to be first formed. 



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