Copy letter from [Robert William Frederick Harrison, Assistant Secretary of the Royal Society]; to Messrs Harrison & Sons 'Please prepare and send with account, to Mr. John Murray, 50 Ablemarle Street, W., electros of Fig. 2, p.138, and Fig. 5, p. 145, (Darwin and Pertz's paper) 'On a new method of estimating the aperture of stomata', Proc. Roy. Soc. B. vol. 84, 1911.' 24 April 1917