CHAP, in.] the Movements of Plants. 553 



a partisan of vital force as Treviranus had to deal with endos- 

 mose as an established principle. Moreover Dutrochet's 

 copious investigations presented such an abundance of in- 

 teresting observations, delicate combinations, and suggestive 

 considerations, that the study of them is still instructive and 

 indeed indispensable to any one who is occupied with such 

 researches. Comparison of his papers in the ' Memoires ' of 

 1837 with what was before known on the mechanical laws 

 of the movements of plants leaves us in no doubt that 

 energetic mental effort had taken the place of the old com- 

 placent absence of thought. 



Still no single movement had as yet been fully explained on 

 mechanical principles ; but by the year 1840 clearer views had 

 been attained on the whole subject ; the co-operation of ex- 

 ternal agencies was in substance recognised, and the different 

 forms of movement were better distinguished, though much 

 still remained to be done in this direction ; and as regards the 

 mechanical changes in the tissue of the parts capable of move- 

 ment, a factor had been given in endosmose which must be 

 taken into account, though it might be necessary to seek a 

 different mode of applying it. 



4. Before proceeding to give some account of the theoretical 

 efforts that were made in this subject between 1840 and 1860, 

 it should be mentioned that new cases of movement in plants 

 had been discovered. Dutrochet observed that the stem in 

 the embryo of Viscum is negatively heliotropic, and had care- 

 fully studied its behaviour ; he opposed the old notion that the 

 geotropic downward curvature is peculiar to main roots, and 

 that that is the reason why they are in 'polar' opposition 

 to the stem, by pointing to the shoots of the rhizomes of Sagit- 

 taria, Sparganium, Typha, and other plants, which at least 

 when young curve downwards with some force ; and on ex- 

 tending Knight's experiment with a rotating wheel he found 

 that the leaves also exhibit a peculiar geotropism. These 

 observations and some new examples of periodical movement 



