_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.
Nothing is more varied than the disposition of these channels in the interior of plants, and their multiplicity indicates a circulatory function as complicated as that of animals.
It is then evident that vegetables have the same physiological functions as animals, but as yet we know those functions very imperfectly. It is very strange that while animal physiology is so far advanced in our day, vegetable physiology is almost in its infancy. We know very well how the digestion of food takes place in man and animals, we know how our blood circulates in a double system of vessels, called arteries and veins, and we know the central organ, the heart, through which the two liquids are carried by this double system. We see and we touch the organs of sensation and motion, that is to say, the nerves. More than this, we distinguish the nerves which produce sensation from those which rule motion. We know that the centre of nervous action in man and animals is double; that its seat is equally in the brain and in the spinal marrow.
Briefly, science has shed its brightest light on all the functions belonging to animal organization, while vegetable physiology remains in obscurity. Notwithstanding the labours of naturalists within the last two centuries, we cannot explain the life of plants with certainty. We cannot positively state how the sap, which is vegetable blood, circulates in their channels. We do not even know with precision whether a tree grows from the outside to the inside, or from the inside to the outside. All the physiological functions in the vegetable kingdom are hidden from us by a thick veil, and it is only by lifting a corner of it with great difficulty that we can catch a few gleams of light through the obscurity. Nevertheless, all unexplained though they be as yet, physiological functions do exist in plants. Considering these numerous functions, it appears entirely impossible that plants should not have received the gift of sensibility. It is difficult to believe, as Linnæus would have us believe, that they possess life, and nothing more.