Plate, figures 14-17 showing growth of roots of plants by unknown artist Figures 14-17 from plate XV showing the growth of roots of various plants included in the authors' experiments. Subject: Botany Published in Philosophical Transactions as 'On the sources of the nitrogen of vegetation; with special reference to the question whether plants assimilate free or uncombined nitrogen'. Received and read by the Royal Society on 21 June 1860. [1860]