256 CIJiCUMNUTATION OF LEAVES. Chap. IV 



5 and 6 p.m. On the next day the leaf stood at only 10° above 

 the horizon at 8.25 a.m., and it remained at about 15^ till past 

 3 p.m.; at 5.40 p.m. it was 23°, and at 9.30 p.m. 58°; so that 

 the rise was more sudden this evening than on the previous 

 one,. and the difference in the angle amounted to 48°. The 

 movement is obviously periodical, and as the leaf stood on the 

 first night at 55°, and on the second night at 58° above the 

 horizon, it appeared very steeply inclined. This case, as we 

 shall see in a future chapter, ought perhaps to have been 

 included under the head of sleeping plants. 

 (33.) Pontederia (sp. ?) (from the highlands of St. Catharina; 



Fig. 118. 



Pontederia (sp. ?) : circumnutiiton of leaf, traced from 4.50 P.M. July 2nd 

 to 10.15 A.M. 4th. Apex of leaf 16J inches from the vertical glass, so 

 tracing greatly magnified. Temp, about 17° C, and therefore rather 

 too low 



Brazil) (Pontederiaceae, Fam. 46). — A filament was fixed across 

 the apex of a moderately young leaf, 7i inches in height, and 

 its movements were traced during 42^ h. (see Pig. 118). On 

 the first evening, when the tracing was begun, and during the 

 night, the leaf descended considerably. On the next morning 

 it ascended in a strongly marked zigzag line, and descended 

 again in the evening and during the night. The movement, 

 therefore, seems to be periodic, but some doubt is thrown on 

 this conclusion, because another leaf, 8 inches in height, 

 appearing older and standing more highly inclined, behaved 

 differently. During the first 12 h. it circumnutated over a 



