LEAT-CLIMBEES. 37 



observations) is in this and the two last species, namely, 1 h. 47m., 

 1 h. 46 m, and 1 h. 48 m. The present species cannot spirally twine, 

 which seems mainly due to the rigidity of its stem. In a 

 very young plant, which did not revolve, the petioles were not 

 sensitive. In older plants the petioles of quite young leaves, and 

 of leaves as much as an inch and a quarter in diameter, are sensi- 

 tive. A moderate rub caused one to curve in 10 m., but others in 

 20m. ; the petioles became straight again in from 5h. 45m. to 8h. 

 Petioles which have naturally come into contact with a stick, some- 

 times take two turns round it. When clasped round a support, 

 they become rigid and hard. The petioles are less sensitive to a 

 weight than in the previous species ; for loops of string weighing 

 *82 of a grain did not cause any curvature, whilst a loop of 

 double this weight (l"64gr.) did act. 



Trop(jeolum elegans. — I did not make many observations on this 

 species. The short and stiff intemodes revolve irregularly, and 

 describe extremely small oval figures ; one was completed in 3 h. 

 A young petiole, when rubbed, became slightly curved in 17 m. ; 

 then much more so ; and was nearly straight again in 8h. 



Tropceolum tuberosum. — The internodes on a plant nine inches 

 high did not move at all ; but on an older plant they moved irregu- 

 larly, and made very small imperfect ovals. These movements could 

 be detected only by being traced on a bell-glass placed over the 

 plant. Sometimes the shoots stood still for hours ; during some 

 days they 'moved only in one direction in a crooked line ; on 

 other days they made small irregular spires or circles, one being 

 completed in about 4 h. The movement of the apex of the shoot, 

 from extreme point to point of the oval, was only about one inch or 

 one and a half ; yet this slight movement brought the petioles 

 into contact with closely surrounding twigs, which were then 

 clasped. With the lessened power of spontaneously revolving, 

 compared with the previous species, the sensitiveness of the 

 petioles is likewise diminished. These, when rubbed a "few 

 times, did not become curved until half an hour had elapsed ; 

 the curvature increased during the next two hours, and then very 

 slowly decreased ; so that the petioles sometimes required 24 h. to 

 become straight again. The petioles of very young leaves can act 

 perfectly; one with the lamina only '15 of an inch in diameter, 

 that is, about a twentieth of the full size, firmly clasped a thin 

 twig : but leaves grown to one quarter of their full size can like- 

 wise act. 



Trop(Solum minus (?). — The intemodes of a variety named 



