CHAP. V. EPINASTY AND HYPONASTY. 269 



the weight of the leaf, and resisted as he believes by apogeo- 

 tropism, at least after the leaf has somewhat diverged. In our 

 observations on the circumnutation of leaves, some were selected 

 which were rather too young, so that they continued to diverge 

 or sink downwards whilst their movements were being traced. 

 This may be seen in the diagrams (Figs. 98 and 112, pp. 232 

 and 249) representing the circumnutation of the young leaves of 

 Acanthus mollis and Pelargonium zonale. Similar cases were ob- 

 served with Drosera. The movements of a young leaf, only I inch 

 in length, of Petunia violacea were traced during four days, and 

 offers a better instance (Fig. Ill, p. 248), as it diverged during 

 the whole of this time in a curiously zigzag line with some of the 

 angles sharply acute, and during the latter days plainly circum- 

 nutated. Some young leaves of about the same age on a plant 

 of this Petunia, which had been laid horizontally, and on another 

 plant which was left upright, both being kept in complete dark- 

 ness, diverged in the same manner for 48 h., and apparently 

 were not aifected by apogeotropism ; though their stems were in 

 a state of high tension, for when freed from the sticks to which 

 they had been tied, they instantly curled upwards. 



The leaves, whilst very young, on the leading shoots of the 

 Carnation (Dianthus caryophyllus) are highly inclined or vertical ; 

 and if the plant is growing vigorously they diverge so quickly 

 that they become almost horizontal in a day. But they move 

 downwards in a rather oblique line and continue for some time 

 afterwards to move in the same direction, in connection, we pre- 

 sume, with their spiral arrangement on the stem. The course 

 pursued by a young leaf whilst thus obliquely descending was 

 traced, and the line was distinctly yet not strongly zigzag ; the 

 larger angles formed by the successive lines amounting only to 

 135, 154, and 163. The subsequent lateral movement (shown 

 in Fig. 96, p. 231) was strongly zigzag with occasional circum- 

 nutations. The divergence and sinking of the young leaves 

 of this plant seem to be very little affected by geotropism or 

 heliotropism ; for a plant, the leaves of which were growing 

 rather slowly {as ascertained by measurement) was laid hori- 

 zontally, and the opposite young leaves diverged from one 

 another symmetrically in the usual manner, without any up- 

 turning in the direction of gravitation or towards the light. 



The needle-like leaves of Pinus pinaster form a bundle whilst 

 young ; afterwards they slowly diverge, so that those on the up- 

 right shoots become horizontal. The movements of one such 



