424.

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424.

p. 216

A leaf with a concave surface seen from the under side and up-side-down will sometimes show itself as half in shade, and half transparent. Thus, if o p is the leaf and the light m and the eye n, this will see o in shadow because the light does not fall upon it between equal angles, neither on the upper nor the under side, and p is lighted on the upper side and the light is transmitted to its under side.  ²¹⁶

Footnotes

216:216 : See Pl. XXVIII, No. 2, the upper sketch on the page. In the original they are drawn in red chalk.