Chap. VIU. 



HELIOTEOPISM. 



i2'3 



Fig. 174. 



e?30' 



S^.m 



no doubt, was due to its then circumnutating in this direction, 

 Similar cases were repeatedly observed, and a dim light rarely 

 or never produced any effect until from a quarter to three- 

 quarters of an hour had elapsed. After 5.15 p.m., by which 

 time the light had become 

 obscure, the hypocotyl 

 began to circumnutate 

 about the same spot. The 

 contrast between the two 

 figures (,172 and 173 J 

 would have been more 

 striking, if they had been 

 originally drawn on the 

 same scale, and had been 

 equally reduced. But the 

 movements shown in Fig. 

 1 72 were at first more mag- 

 nified, and have been re- 

 duced to only one-half of 

 the original scale; whereas 

 those in Fig. 173 were at 

 first less magnified, and 

 have been reduced to a 

 one-third scale. A tracing 

 made at the same time 

 with the last of the 

 movements of a second 

 hypocotyl, presented a 

 closely analogous appear- 

 ance ; but it did not bend 

 quite so much towards the 

 light, and it circumnu- 

 tated rather more plainly. 

 I'halaris Canariensis. — 

 The sheath-like cotyledons 

 of this monocotyledonous 

 plant were selected for 

 trial, because they are very sensitive to light and circumnutate 

 well, as formerly shown (see Fig. 49, p. 63). Although we felt 

 no doubt about the result, some seedlings were first placed 

 before a south-west window on a moderately bright morning, and 

 the movements of one were traced. As is so common, it moved 



8h5'a.m.SepJS.'^ 



I'halaris Canariensis: heliotropic movement 

 and circumnutation of a rather old coty- 

 ledon, towards a dull lateral light, traced 

 on a horizontal glass from 8.15 A.M. Sept. 

 16th to 7.45 A.M. 17th. Figure reduced 

 to one-third of original scale. 



