{188} Fritz Müller informs me that he saw in the forests of South Brazil numerous black strings, from some lines to nearly an inch in diameter, winding spirally round the trunks of gigantic trees. At first sight he thought that they were the stems of twining plants which were thus ascending the trees: but he afterwards found that they were the aërial roots of a Philodendron which grew on the branches above. These roots therefore seem to be true twiners, though they use their powers to descend, instead of to ascend like twining plants. The aërial roots of some other species of Philodendron hang vertically downwards, sometimes for a length of more than fifty feet. {197} Quoted by Cohn, in his remarkable memoir, “Contractile Gewebe im Pflanzenreiche,” ‘Abhandl. der Schlesischen Gesell. 1861, Heft i. s. 35. {198} Such slight spontaneous movements, I now find, have been for some time known to occur, for instance with the flower-stems of _Brassica napus_ and with the leaves of many plants: Sachs’ ‘Text-Book of Botany’ 1875, pp. 766, 785. Fritz Müller also has shown in relation to our present subject (‘Jenaischen Zeitschrift,’ Bd. V. Heft 2, p. 133) that the stems, whilst young, of an Alisma and of a Linum are continually performing slight movements to all points of the compass, like those of climbing plants. {199} Mr. Herbert Spencer has recently argued (‘Principles of Biology,’ 1865, p. 37 et seq.) with much force that there is no fundamental distinction between the foliar and axial organs of plants. {200} Annales des Sc. Nat. 4th series, Bot. tom. vi. 1856, p. 31. {202} Moquin-Tandon (Eléments de Tératologie. 1841, p. 156) gives the case of a monstrous bean, in which a case of compensation of this nature was suddenly effected; for the leaves completely disappeared and the stipules grew to an enormous size.