250 CIRCUMNUTATIOX OF LEAVES. CHAP. IT. 



or exclusively due to the straightening of the blade, and not to 

 the movement of the petiole. We may therefore conclude that 

 the leaves of Acanthus circumnutate periodically, falling in the 

 morning and rising in the afternoon and night. 



(24.) Cannabis sativa (Cannabinese, Fam. 195). We have 

 here the rare case of leaves moving downwards in the evening, 

 but not to a sufficient degree to be called sleep.* In the early 

 morning, or in the latter part of the night, they move upwards. 

 For instance, all the young leaves near the summits of several 

 stems stood almost horizontally at 8 A.M. May 29th, and at 

 10.30p.sr. were considerably declined. On a subsequent day two 

 leaves stood at 2 P.M. at 21 and 12 beneath the horizon, and at 

 10 P.M. at 38 beneath it. Two other leaves on a younger plant 

 were horizontal at 2 P.M., and at 10 P.M. had sunk' to 36 beneath 

 the horizon. With respect to this downward movement of the 

 leaves, Kraus believes that it is due to their epinastic growth. 

 He adds, that the leaves are relaxed during the day, and tense 

 at night, both in sunny and rainy weather. 



(25.) Pinus pinnster (Coniferae, Fam. 223). The leaves on the 

 Biimmits of the terminal shoots stand at first in a bundle almost 

 upright, but they soon diverge and ultimately become almost 

 horizontal. The movements of a young leaf, nearly one inch in 

 length, on the summit of a seedling plant only 3 inches high, 

 were traced from the early morning of June 2nd to the evening 

 of the 7th. During these five days the leaf diverged, and its apex 

 descended at first in an almost straight line ; but during the two 

 latter days it zigzagged so much that it was evidently circumnu- 

 tating. The same little plant, when grown to a height of 5 inches, 

 was again observed during four days. A filament was fixed 

 transversely to the apex of a leaf, one inch in length, and which 

 had already diverged considerably from its originally upright 

 position. It continued to diverge (see A, Fig. 113), and to 

 descend from 11.45 A.M. July 31st to 6.40 A.M. Aug. 1st. On 

 August 1st it circumnutated about the same small space, and 

 again descended at night. Next morning the pot was moved 

 nearly one inch to the right, and a new tracing was begun (B), 

 From this time, viz., 7 A.M. August 2nd to 8.20 A.M. on the 4th, 



* Wo were led to observe this Flcra, 1879, p. 66. We regret that 



pliint by Dr. Carl Kraus' paper, we cannot fully understand p;irtu 



' Beitriijre zur Kentuias der Bewe- of this paper, 

 eii Wuchscnder Laubbliitter,' 



