Be it positive or negative, phototropism appears to us as a purely physical directive reaction; that is to say, innate, automatic, independent <of all choice and consequently of all psychic phenomena.
It is innate because all sensitive animals are phototropic from birth, and the reactions which they present are not the result of an individual education. Neither do they seem to result from the education of the species in the course of its history. Loeb cites on this subject the examples of the tree-boring caterpillars of Cossus ligni-perda and a little marine crustacean, Cuma rath-kei, common on our shores. Both are endowed with a very strong positive phototropism, but live, in complete obscurity, the first in the long galleries it makes in willow, apple, and a number of other trees which it kills, while the other is a burrowing animal which nests deep within the ooze.