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 always 

 say confidently to those philosophers who wish to believe 

 that everything depends upon mechanics, and forces 

 which act mechanically " Tell us, ye slanderers, are you 

 then acquainted with the fundamental theory of the whole 

 of your mechanics; do you understand the cause of 

 motion even in the slightest degree ? Is it not the most 

 incomprehensible of all the phenomena with which we 

 are surrounded?" And even if it were answered that it 

 was the first, the most common, and the most certain 

 empirical knowledge upon which anything could be based 

 with certainty, it might be easily replied, that the same 

 was also the case with vitality, for we cannot even start 

 the question of the cause of motion without living. What 

 has just been stated might be recommended to many 

 philosophers, especially in foreign countries, as a subject 

 for careful consideration, when they urge mechanical ex- 

 planations to the very utmost when, as it were, they 

 are 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 fluids 

 in the cells and vessels which permeate the membranes, 

 fill and distend the cells, and produce movements by 

 means of this distension, and even by flowing out pro- 

 duce collapse and motion in the opposite direction. Yet 

 the causes of the phenomena of endosmose and exosmose, 

 upon which this theory is based, have by no means been 

 ascertained; it has certainly not been proved that the 

 exchange of matters in solution through the unvitalised 

 membrane, which we find in these experiments, occurs 

 through the living membrane of the cells in plants, for 

 the simple reason, that we do not find that those cells 

 which are situated near each other contain different fluids, 

 by means of which this exchange could be effected ; we 

 cannot understand how the gradual influx and egress 



