432 



MODIFIED CIRCUMNUTATION. CHAP. VIII. 



ellipse was completed between 3 P.M. and about 5.30 P.M., 

 the hypocotyl still bending towards the light. The hypocotyl 



Fig. 178. 



was straight and upright in the morn- 

 ing, but by 6 P.M. its upper half was 

 bowed towards the light, so that the 

 chord of the arc thus formed stood at 

 an angle of 20 with the perpendicular. 

 After 6 P.M. its course was reversed 

 through the action of apogeotropism. 

 and it continued to bend from the 

 window during the night, as shown by 

 the broken line. On the next day it 

 was kept in the dark (excepting when 

 each observation was made by the aid 

 of a taper), and the course followed 

 from 7 A.M. on the 8th to 7.45 A.M. on 

 the 9th is here likewise shown. The 

 difference between the two parts of the 

 figure (177), namely, that described 

 during the daytime on the 7th, when 

 exposed to a rather dim lateral light, 

 and that on the 8th in darkness, is 

 striking. The difference consists in the 

 lines during the first day having been 

 drawn out in the direction of the light. 

 The movements of the other seedling, 

 traced under the same circumstances, 

 were closely similar. 



Apheliotropism. We succeeded in 

 observing only two cases of aphelio- 

 tropism, for these are somewhat rare ; 

 and the movements are generally so 

 slow that they would have been very 

 troublesome to trace. 



Bignonia capreolata. No organ of 

 any plant, as far as we have seen, bends 

 away so quickly from the light as do 

 the tendrils of this Bignonia. They 

 are also remarkable from circum- 

 nutating much less regularly than 

 most other tendrils, often remaining 

 stationary; they depend on apheliotropism for coming into 



Bignonia capreolata : aphe- 

 liotropic movement of a 

 tendril, traced on a hoi-i- 

 zontal glass from 6.45 

 A.M. July 19th to 10 A.M. 

 20th. Movements as 

 originally traced, little 

 magnified, here reduced 

 to two-thirds of the 

 original scale. 



