233 
Suppose that the leaf-margin after acquiring the shape as 
determined above ceases to be flexible, then the action between 
two contiguous portions of the margin will not be entirely 
tangential, but in addition to the tension + there will exist a 
normal strain N and a mechanical couple P tending to wrench 
the margin. Let 7,, p,,, be the tension, the power of growth, 
and the velocity respectively at the time when the margin 
acquires its shape, then for portions of the margin subject to 
the opposing resistance of the current, 
ds pale) 
dp 1 
Whe oliat 
Po 5 7% 810 p 
The new equations of equilibrium will be 
—7+ (r+ 67) cos 6p —(N+ 6K) sin 6h = 0, 
N— (N+ 6N) cos 6h — (7 + Gr) sin Of 
1 ; 6 
+(p—gov'sin' $s aae 0, 
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4 “+ V+ 6 A 
‘ %, Uf 
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4 a / 
‘ mere Vi 
\ gov" sin? p. b8-Y 
‘ ben 
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Pp 
and by taking moments about the point P 
P—(P+6P) —-(N+6N) 6s=0, 
