Gottfried Reinhold Treviranus  

"Of all apparently voluntary movements of plants, the direction of their boughs and of the upper surface of their leaves towards the light and towards moist heat, and the twining movements of creepers round their supports, are the most universal. In this last phenomenon especially there is something which resembles animal movements. While growing, creepers, it is true, if left to themselves, describe circles with their tips and by this means reach an object near at hand. But it is no merely mechanical cause that induces them to adapt their growth to the form of the object they have thus reached. The cuscuta does not twine round every kind of support: for instance, limbs of animals, dead vegetable matter, metals and inorganic substances are not used for this purpose, but only living plants, and not even all kinds—not mosses, for instance—only those from which it can extract nourishment by its papillæ; and these attract it from a considerable distance."--Treviranus cited in On the Will in Nature (1836) by Arthur Schopenhauer