CHAP. VIII. 



HELIOTEOPISM. 



427 



Fig. 174. 



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) 



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. Solaris Canariensis: heliotropic movement 

 U7. T xv ' an d circumnutation of a rather old coty- 



Phalans Canariensis.- ledon? towards a dull lateral %ht? trace ' d 



The sheath-like cotyledons on a horizontal glass from 8.15 A.M. Sept. 

 of this monocotyledonous 16th to 7 - 45 A - M - 17th - Figure reduced 

 plant were selected for to one-third of original scale. 



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 



