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-10,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 cell, 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,? Ewart.3 Hydroxyland nascent Hydrogen are supposed by others 
to be first formed. 
30 
