42 



MB. DAEWIN ON CLIMBING PLANTS. 



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regularly at an average rate of 3 h. 26 m. The shoots, however, 

 sometimes stand still. It is considered a greenhouse plant ; but 

 when kept there, the petioles took several days to clasp a stick : 

 in the hothouse a stick was clasped in 7 h. ' In the greenhouse a 



Fig. 3. 



Solanum jasminoides^ -with one of its leaves clasping a stick. 



petiole was not affected by a loop of string, suspended during 

 several days and weighing 2^ grains ; in the hothouse one 

 was made to curve by a loop weighing l'64i (and, on the 

 removal of the string, became straight again), but was not at 

 all affected by another loop weighing -82 of a grain. We have seen 

 that the petioles of some other leaf-climbing plants were affected 

 by one-thirteenth of this latter weight. In this plant, and in no 

 other leaf-climber seen by me, a leaf grown to its full size was 

 capable of clasping a stick ; but the movement was so extraordi- 

 narily slow that in the greenhouse the act required several weeks ; 

 but on each succeeding week it was clear that the petiole became 

 more and more curved, until finally it firmly clasped the stick. 



When the flexible petiole of a half- or a quarter-grown leaf has 

 clasped any object, in three or four days it increases much in 

 thickness, and after several weeks becomes wonderfully hard and 

 rigid ; so that I could hardly remove one from its support. On 

 comparing a thin transverse slice of this petiole with one from 

 the next or older leaf beneath, which had not clasped anything, 

 its diameter was found to be fully doubled, and its structure 

 greatly changed. In two other petioles similarly compared, and 



