Stem '^ Separation Stalk 

 tissue layer tissue 



THE FALL OF A LEAF 



Plants that regularly drop their leaves in the autumn form a special layer of cells in 

 the stalk of each leaf, and sometimes of each leaflet of a compound leaf. These 

 cork cells are thin-wailed and turgid. Their contents break down into a mucilaginous 

 mass, which dries up. A slight movement is now sufficient to break the fibrovascular 

 bundle at this point, and as the leaf is removed the exposed surface becomes a 

 self-healing scar 



Organisms withstand heat and dryness very unequally. Man, for in- 

 stance, dries out rather quickly in the hot, dry desert, although the evapora- 

 tion from the skin and lungs lowers the body temperature and protects the 

 protoplasm against becoming too hot. But the lost water has to be replaced, 

 or the protoplasm will suffer other injury. During the Second World War 

 many men who were saved from torpedoed ships, or from planes forced 

 down on the ocean, later died for want of water. This was an urgent prob- 

 lem, and several lines of research were followed to solve it. Before any 

 practicable means had been worked out for making sea water fit to drink, 

 Gifford Pinchot (1865- ) sought for fresh water in the life of the sea. 

 Pinchot, who started the conservation movement, showed by experiments 

 that the juice squeezed from the flesh of salt-water fish could serve men as 

 drink in place of fresh water, as the raw flesh may serve as food. As a 

 result of these experiments, airplane rafts and steamship lifeboats were 

 equipped with fishing tackle and instructions for living on what the ocean 

 yields. 



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