Chap. Vni. 



HELIOTBOPISM. 



427 



ff^.ra'C 



no doubt, was due to its then cirounmutating in this direction. 

 Similar cases were repeatedly observed, and a dim light rarely 

 or never produced any eflfect 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. 

 172 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- 



Shg'a.m.SeplB.^!' 



tated rather more plainly. P^w^aris Canariensis: heliotropie movement 

 Ti-L 1 • n ■ • and circumnutation of a rather old cotv- 



Phalaris Canariensis.- j^^^^^ ^^^^^^ , ^^H j^j^^j Ugj^j^ ^^^^^. 



The sheath-Hke cotyledons 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. 



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 



