56 LEAF-OLIMBBES. Chap. U. 



this latter species it has diminished in the basal pait 

 of the main petiole, in wnich alone it resided in G. 

 montana; whilst it has increased in the abruptly bent 

 terminal portion. 



Clematis Jldmmula. — The rather thick, straight, and 

 stiff shoots, whilst growing vigorously in the spring, 

 make small oval revolutions, following the sun in their 

 course. Four were made at an average rate of 3 hrs, 

 45 m. The longer axis of the oval, described by the 

 extreme tip, was directed at right angles to the line 

 joining the opposite leaves ; its length was in one case 

 only If, and in another case If inch; so that the 

 young leaves were moved a very short distance. The 

 shoots of the same plant observed in midsummer, 

 when growing not so quickly, did not revolve at all. 

 I cut down another plant in the early summer, so that 

 by August 1st it had formed new and moderately 

 vigorous shoots; these, when observed under a bell- 

 glass, were on some days quite stationary, and on 

 other days moved to and fro only about the eighth of 

 an inch. Consequently the revolving power is much 

 enfeebled in this species, and under unfavourable cir- 

 cumstances is completely lost. The shoot must depend 

 for coming into contact with surrounding objects on the 

 probable, though not ascertained spontaneous move- 

 ment of the leaves, on rapid growth, and on movement 

 from the wind. Hence,,perhaps, it is that the petioles 

 have acquired a high degree of sensitiveness as a com- 

 pensation for the little power of movement in the shoots. 



The petioles are bowed downwards, and have the 



