CHAP, in.] the Movements of Plants. 551 



of tendrils and climbing-plants was one of von MohPs best works, 

 and altogether the best that appeared on the subject before 

 Darwin wrote upon it in 1865; at the same time it must 

 be said that von Mohl did not explain the exact mechanical 

 processes in the tissues, for he assumed a sensitiveness in both 

 cases which causes the winding round the support, and thought 

 that this sensitiveness must be conceived of ' dynamically ' and 

 not ' mechanically.' Nevertheless von Mohl conducted his in- 

 vestigation up to this point according to strict rules of induc- 

 tive science, and studied the facts which were capable of being 

 established by observation and experiment with an exactness 

 such as had not yet been applied to any case of movement in 

 plants. It was a genuine production of its author, strictly 

 inductive up to the point at which deduction became neces- 

 sary. Von Mohl pointed out in it essential differences in the be- 

 haviour of tendrils and climbing plants, and the corresponding 

 distinction between the organs which have to be considered in 

 each case, and he made the important discovery that contact 

 with the support acts as a stimulus on the tendril, though he 

 was wrong in supposing that the climbing stem also is similarly 

 affected. He at once assented to Dutrochet's new view, that 

 it is not the vascular bundles but the layers of parenchyma 

 which produce the movements. He distinctly rejected the 

 notion constantly repeated, though with some hesitation, since 

 the time of Cesalpino, that tendrils and climbing-plants * seem 

 to seek for ' their supports, as also the idea which many had 

 adopted without reflection from Grew, that the varying direc- 

 tion of a climbing-stem is due to the varying influence of the 

 course of the sun and moon, and showed that the movements 

 of nutation in the stem are sufficient to explain the apparent 

 seeking for the support ; it is true that he did not fully explain 

 the corresponding phenomena in tendrils, but he saw enough 

 to set aside the old ideas. We must not here go further into 

 his many, and for the most part excellent, observations ; some 

 of course had afterwards to be corrected, but the important 



