PHYSIOLOGICAL BOTANY. 195 



occurring in endosmosis and exosmosis can produce 

 rapid movements, especially those of Mimosa pudica, to 

 which Dutrochet applies his theory ; lastly, it cannot be 

 explained by mechanical laws how this expansion and 

 contraction of the cells becomes capable of raising whole 

 portions of plants. Still this is repeated by the majority, 

 and De Candolle was once at their head ; but I must 

 cease here, to avoid falling into the very error that I have 

 attributed to others. 



Is it not better, instead of retarding the progress of 

 science by such explanations and their details, to recur at 

 once to a vital force, the determination of the laws of which 

 will remain our object, and our not unfounded hope ? 



To a certain extent, but to a certain extent only, has 

 Liebig returned to the ordinary path in regard to the 

 vital force. In his book, * Organic Chemistry in its Ap- 

 plication to Physiology and Pathology' (translated by 

 Dr. Gregory, London, 1842), in the third part, speaking 

 of the phenomena of motion in the animal organism 

 (p. 196), he says : " If the vital phenomena be considered 

 as manifestations of a peculiar force, then the effects of 

 this force must be regulated by certain laws, which laws 

 may be investigated ; and these laws must be in harmony 

 with the universal laws of resistance and motion, which 

 preserve in their courses the worlds of our own and other 

 systems, and which also determine changes of form and 

 structure in material bodies, altogether independently of 

 the matter in which vital activity appears to reside, or of 

 the form in which vitality is manifested." The author is 

 by no means clear in his views of the pretended vital 

 force. What is meant by " must be in harmony ?" Are 

 they the same, or do they only resemble each other ? We 

 do not see why they might not be directly opposed, or 

 totally different. But the author's views are not clear 

 even upon a purely physical force, the attraction of 

 gravitation. He says (1. c. p. 201) : " If it (the stone) 

 fall from a certain height, it makes a permanent impres- 

 sion on the spot on which it falls ; if it fall from a still 



