44 MR. DARWIN ON CLIMBING PLANTS. 



anticipated that so lowly a plant would have been a climber. This 

 it effects by the aid of the main and lateral petioles of its com- 

 pound leaves ; even the much -flattened terminal portion of the 

 petiole can seize a support. I have seen a substance as soft as a 

 withered blade of grass caught. Petioles which have clasped any 

 object ultimately became rather thicker and more cylindrical. 

 On lightly rubbing with a twig several petioles, they became per- 

 ceptibly curved in lb. 15m., and subsequently they straightened 

 themselves. A stick gently placed in the angle between two sub- 

 petioles caused movement in 7h., and was almost clasped in 9h. A 

 loop of thread, weighing one-eighth of a grain, caused, after 12 h. 

 and before 20 h. had elapsed, a considerable curvature ; but the 

 petiole never fairly clasped the thread. The young intemodes 

 arc in continual movement ; the movement is considerable, but 

 very irregular in course; a zigzag line, or a spire crossing itself, 

 or a figure of 8 is formed ; the course during 12 h., being traced 

 on a bell-glass, apparently represented about four ellipses. The 

 leaves themselves also move spontaneously, the main petiole curv- 

 ing itself in accordance with the movement of the intemodes ; so 

 that when the latter move to one side the petiole is curved to 

 that side, then, becoming straight, is curved to the opposite side. 

 Thus a wider space is swept for a support to be clasped. The 

 movement, however, is small, as could be seen when the shoot 

 was securely tied to a stick and the leaf alone allowed to move. 

 The leaf in this case followed an irregular course, like that made 

 by the young intemodes. 



Adlumia cirrhosa. — I raised some plants late in the summer ; 

 they formed magnificent leaves, but threw up no central stem. 

 The first-formed leaves were not sensitive ; but some of the later 

 leaves were sensitive, but only towards their extremities, and were 

 able to clasp sticks. This could be of no service to the plant, as 

 these leaves rose from the ground ; but it showed what the future 

 character of the plant would be when it had grown tall enough to 

 climb. The tip of one of these ground leaves, whilst young, de- 

 scribed in 1 h. 36 m. a narrow ellipse, open at one end, and exactly 

 three inches in length ; a second ellipse was broader, more irre- 

 gular, and shorter, viz. only 2| inches in length, and was com- 

 pleted in 2h. 2 m. From analogy with Fumaria and Corydalis, I 

 have no doubt that the intemodes have the power of revolving. 



may be observed that the enlarged and clasped petiole of the Solatium, with its 

 closed ring of woody vessels, has become much more cylindrical than it was in 

 its original unclasped condition. 



