Sunshine, Rain, and Wind 



long fine point which many of them possess. This acts 

 as a spout or gutter, draining off the water from the 

 rest of the surface. 



But to really appreciate the trials of leaves and the 

 extraordinary beauty of their mechanism, one has to 

 watch a tree in full leaf exposed to a strong westerly 

 gale. Everything is in movement, bending and swaying 

 backwards and forwards ; great strain is thrown on the 

 roots, which will be at one moment buttresses and the 

 next acting as taut cables resisting the pull of the 

 return swing. Every detail in leaf-shape and arrange- 

 ment, in habit of branching, and in the character of the 

 tissues is obviously so contrived as to resist the enor- 

 mous stresses and strains that are at work. 



No two trees have quite the same ideals. In the 

 ash the leaf-stalk yields, and each leaflet folds at its 

 base and becomes acute-angled. In the birch every- 

 thing swings so that every leaf becomes edgewise to 

 the storm. The beech is far more rigid and stiff, yet 

 the leaf-edges twist into the right position. 



Some careful experiments have brought out both the 

 ingenious contrivances of these leaves and also their 

 extraordinary strength. These were carried out with 

 artificial storms produced by electric ventilators, and are 

 unfortunately too detailed to give in full.-^ 



In the black poplar, e.g.y the leaf-folds and different 

 leaves cling together, in such a way that a leaf surface 

 of over 10 square centimetres (1.55 square inch) 

 has, when exposed to a gale of 10 metres (32.8 feet) 

 per second, only 1.2 square centimetre (.186 square 

 inch) of area. 



A sycamore leaf which had a surface of 164 square 

 centimetres (25.42 square inches) was found to be un- 

 able to bear a weight of 827 gr. (if lb.). But even 

 in a hurricane of 60 feet per second, the force of the 



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