408 TRANSMITTED EFFECTS OF LIGHT. CHAP. IX 



with a mixture of oil and lamp-black, and were then 

 exposed before a window ; others similarly treated were 

 afterwards tried in darkness. These cotyledons soon 

 became plainly bowed towards the blackened side, 

 evidently owing to the grease on this side having' 

 checked -their growth, whilst growth continued on the 

 opposite side. But it deserves notice that the curva- 

 ture differed from that caused by light, which ulti- 

 mately becomes abrupt near the ground. These 

 seedlings did not afterwards die, but were much injured 

 and grew badly. 



LOCALISED SENSITIVENESS TO LIGHT, AND ITS 

 TRANSMITTED EFFECTS. 



Phalaris Canariensis. Whilst observing the accu- 

 racy with which the cotyledons of this plant became 

 bent towards the light of a small lamp, we were 

 impressed with the idea that the uppermost part deter- 

 mined the direction of the curvature of the lower part. 

 When the cotyledons are exposed to a lateral light, 

 the upper part bends first, and afterwards the bending 

 gradually extends down to the base, and, as we shall 

 presently see, even a little beneath the ground. 

 This holds good with cotyledons from less than 

 1 inch (one was observed to act in this manner which 

 was only '03 in height) to about '5 of an inch in 

 height ; but when they have grown to nearly an inch 

 in height, the basal part, for a length of '15 to '2 of 

 an inch above the ground, ceases to bend. As with 

 young cotyledons the lower part goes on bending, 

 after the upper part has become well arched towards 

 a lateral light, the apex would ultimately point to 

 the ground instead of to the light, did not the upper 

 part reverse its curvature and straighten itself, as 



