410 



MR. F. D.VRWIN ON THE POSITION OF 



towards the light ; and it will bo seen that i. sunk and ii. rose, 

 both therefore approaching the diaheliotropic plane. 



When a cherry-plant is placed in the normal position in the 

 dark, it behaves very differently from Ranunculus Ficaria, whose 

 leaves bend apogeotropically upwards when released from the 

 stimulus of vertical light which keeps them horizontal. Under 

 similar conditions the leaves of the cherry remain almost in un- 

 altered positions, and certainly exhibit no such well-marked 

 rising as occurs in It. Ficaria, and, according to Frank, in other 

 radicle leaves*. 



Experiment 2 (Table XI.). — A plant whose leaves had been epi- 

 nastieally curved downward in a way to be presently described, was 

 placed in a tall cylinder blackened inside, where the light was faint 

 enough to cause seedling-cabbages growing in it to be " drawn 

 up." This was done on the morning of May 12th, after the angles 

 given below had been measured. It will be seen that by the next 

 evening there had been a considerable rise, owing to apogcotro- 

 pism ; and if the experiment had been on M. Ficaria, the apogeo- 

 tropic movement would have been continued and the leaves would 

 have become nearly vertical. But although the plant was now 

 (May 13th, 6.45 p.m.) put in the dark until May 17th, the leaves 

 did not become much raised above the horizon, and some went 

 slightly below it. 



Table XL 



Date. 



Leaf i. 



Leaf ii. j Leaf iii. 



Leaf iv. 



Leaf v. 



May 12, 8.33 a.m. -32 



o o 

 -30 -15 



o 

 -47 



o 

 -28 



Now (May 12th) placed in dull light. 





May 13, 6.45 p.m. —27 1 —11 — 4 — 



'4-27 



Now (May 13th) placed in the dark. 





May 17, 10.20 a.m. - + 9 1 + 7 



-20 



- 7 



In another experiment a plant growing out of doors, and having 

 three approximately horizontal leaves, was placed in the dark in 

 the afternoon of May 4th ; it remained in the dark till the morning 

 of May 7th j and the leaves exhibited no rising, but, on the con- 

 trary, sank to 12°, 28°, and 25° below the horizon. 



* Frank does not mention the cherry ; he says that the leaves of trees vary 

 in their hehaviour when placed in darkness. 



