These roots therefore seem to be true twiners,
though they use their powers to descend, instead of to ascend like
twining plants. The aerial roots of some other species of
Philodendron hang vertically downwards, sometimes for a length of
more than fifty feet.
{44} Quoted by Cohn, in his remarkable memoir, "Contractile Gewebe
im Pflanzenreiche," 'Abhandl. der Schlesischen Gesell. 1861, Heft i.
s. 35.
{45} 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 Muller 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.
{46} 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.
{47} Annales des Sc. Nat. 4th series, Bot. tom.
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