He familiarised himself more and more with the endless variety of plants and trees, of the earth and the sky at the differing hours of the day: he made his forms even more precise. He wished to paint the organic life of inanimate nature--the life which heaves unconsciously everywhere, sighing in the air, streaming from the bosom of the earth, and vibrating in the tiniest blade of grass as positively as it palpitates through the branches of the old oaks. These trees and herbs are not human, but they are characterised by their peculiar features, just as though they were men. The poplars grow like pyramids, and have green and silvered leaves, the oaks dark foliage and gnarled far-reaching boughs. The oaks stand fixed and immovable against the storm, whilst the slender poplars bend pliantly before it. This curious distinction in all the forms of nature, each one of which fulfils a course of existence like that of man, was a problem which pursued Rousseau throughout his life as a vast riddle. Observe his trees: they are not dead things; the sap of life mounts unseen through their strong trunks to the smallest branches and shoots, which spread from the extremity of the boughs like clawing fingers. The soil works and alters; every plant reveals the inner structure of the organism which produced it. And this striving even became a curse to him in his last period. Nature became for him an organism which he studied as an anatomist studies a corpse, an organism all the members of which act one upon the other according to logical laws, like the wheels of a machine; and for the proper operation of this machine the smallest plants seemed as necessary as the mightiest oaks, the gravel as important as the most tremendous rock. [Illustration: _Hanfstaengl._ COROT. THE DANCE OF THE NYMPHS.]