"The sleep of plants vaguely resembles that of animals. It is a remarkable circumstance that the slumbering leaf appears to wish to return to the epoch of its infancy. It folds itself almost as it was when in the bud, before it burst out, as it was in the lethargic sleep of winter, sheltered beneath its strong scales, or wrapped up in its warm down. One would think that the plant was trying every night to resume the position which it occupied in its early time, just as the sleeping animal gathers himself together, and folds his limbs as they were folded in his mother's womb."[15] Is it possible to deny the possession of sensibility to creatures which give us alternate sign of repose and of activity, and who have the power of accommodating themselves to various external impressions? Fatigue cannot possibly be anything but the consequence of the experience of an impression. 3. Numerous physiological functions are fulfilled by plants as well as by animals; and when we consider the number and variety of these functions, it is difficult to understand how, if animals be, as the common consent of mankind declares them, possessed of sensibility, plants can be destitute of it. An ancient philosopher defined plants as _animals with roots_. We shall see, on examining the variety of functions performed by vegetables, whether this philosopher was not a far-seeing, wise man. It would be difficult to name any function with which the animal is invested that the vegetable does not possess in a less degree. _Respiration_, for instance, is equally a property of plants and of animals. Among the latter, respiration consists in the absorption of the oxygen of the air and the emission of carbonic acid gas and watery vapour; among plants it consists in the emission of carbonic acid gas and watery vapour during the night, and during the day, under the influence of sunlight, of the emission of oxygen proceeding from the decomposition of carbonic acid. The function is evidently of the same nature in both the natural kingdoms. _Exhalation_ is a function common to vegetables and to animals. By the stomata of leaves, as by the pores of the skin of animals, watery vapour and various gases, according to the vital phenomena which take place in the interior of the tissues, are constantly being disengaged. _Absorption_ takes place in both kingdoms. If you pour water on the lower surface of a leaf, you will see that it will be absorbed with great rapidity. Sprinkle a bouquet of flowers with water, and the freshness of the withered blossoms will revive. Absorption is even more active in vegetable than in animal tissues. The circulation of liquids in the interior of plants is accomplished by a complicated system of channels and vessels of every order and of every calibre, absorbent vessels, exhalant vessels.