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, eg., 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, (13 Ib.). But even 
in a hurricane of 60 feet per second, the force of the 
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