194

PHYSIOLOGICAL BOTANY.

rarely declared a phenomenon to be incomprehensible,whilst they have frequently erred in the contrary direc-tion ; but supposing they had done so, they could alwayssay confidently to those philosophers who wish to believethat everything depends upon mechanics, and forceswhich act mechanically—“ Tell us, ye slanderers, are youthen acquainted with the fundamental theory of the wholeof your mechanics; do you understand the cause ofmotion even in the slightest degree ? Is it not the mostincomprehensible of all the phenomena with which weare surrounded ?” And even if it were answered that itwas the first, the most common, and the most certainempirical knowledge upon which anything could be basedwith certainty, it might be easily replied, that the samewas also the case with vitality, for we cannot even startthe question of the cause of motion without living. Whathas just been stated might be recommended to manyphilosophers, especially in foreign countries, as a subjectfor careful consideration, when they urge mechanical ex-planations to the very utmost—when, as it were, theyare suspended in the air without any support. Dutrochet may serve as an example; he attempts to explain me-chanically all the motions of plants, by means of endos-mose and exosmose, by the influx and egress of the fluidsin the cells and vessels which permeate the membranes,fill and distend the cells, and produce movements bymeans of this distension, and even by flowing out pro-duce collapse and motion in the opposite direction. Yetthe causes of the phenomena of endosmose and exosmose,upon which this theory is based, have by no means beenascertained; it has certainly not been proved that theexchange of matters in solution through the unvitalisedmembrane, which we find in these experiments, occursthrough the living membrane of the cells in plants, forthe simple reason, that we do not find that those cellswhich are situated near each other contain different fluids,by means of which this exchange could be effected; wecannot understand how the gradual influx and egress