Natural History 607 



vides for the effective distribution of water to all the living cells. 

 The lower skin of the leaf is pierced by minute openings the 

 stomata so numerous that there may be one hundred thousand 

 to the square inch. Through these minute openings water vapour 

 flows out, and carbon dioxide flows in. They communicate with 

 a system of air spaces in the leaf which allows a supply of the gas 

 to reach every cell. The leaf -cell is the actual laboratory in which 

 the upbuilding of food takes place; it includes, embedded in the 

 living matter, numerous biscuit-shaped green bodies (chlorophyll 

 corpuscles) , whose function it is to absorb and transform the light 

 energy. 



The flatness of the leaf means a large absorbing surface, and 

 the arrangement of leaves is suited to avoid mutual shading, and 

 consequent loss of light. The leaves of ivy on a wall look like a 

 mosaic, small leaves fitting into the space left by the larger ones. 

 The branches of trees are scaffoldings which spread the foliage to 

 the light, and all the devices of twining, climbing, and rambling 

 plants serve the same end namely, the capture of parts of the 

 sunlight. 



To the leaf -cell, then, there flows water with salts through 

 the veins, and carbon dioxide through the stomata and air spaces. 

 In the cell there is an energy transformer and absorber, the 

 chlorophyll. In the cell, too, there is protoplasm, the physical 

 basis of life, which utilises the raw materials and the energy of 

 light, so as to transform the carbon dioxide and water into simple 

 organic compounds of carbohydrate nature. In this process there 

 is a liberation of oxygen, which passes out by the little openings. 

 The formation of these simple carbohydrates is the fundamental 

 process of plant nutrition, and indeed of life in general on our 

 globe, for from them are derived all other organic compounds 

 whatever, in animal as well as in plant. 



It will be noted that this process of photosynthesis is the exact 

 reverse of the vital combustion which all living implies, where 

 organic substance is combined with oxygen, breaks down into 



