Chap. II. 



SOLAN CM. 



73 



weighing only -82 of a grain (53*14 mg.) We have 

 seen that the petioles of some other leaf-climbing plants 

 are affected by one-thirteenth of this latter weight. In 

 this species, and in no other leaf-climber seen by me, 

 a full-grown leaf is capable of clasping a stick ; but in 

 the greenhouse the movement was so extraordinarily 



Fig. S. 

 Solanuvijatmi'noidet, with one of its petioles clasping a stick. 



slow that the act required several w r eeks ; on each 

 succeeding week it was clear that the petiole had 

 become more and more curved, until at last it firmly 

 clasped the stick. 



The flexible petiole of a half or a quarter grown 

 leaf which has clasped an object for three or four 

 days increases much in thickness, and after several 

 weeks becomes so wonderfully hard and rigid that it 



