430 



MB. F. DABWIN OX THE POSITION OF 



Frank*, in his ' Wagerechte Kichtung von Pflanzentheilen,' 

 pp. 45, 46, speaks of the leaves of S. Ficaria, in common with a 

 number of other radical leaves, as tending to place themselves at 

 right angles to the light when laterally illuminated ; the leaves 

 which point away from the light rising up, while those directed 

 towards it sink, so that both approach the diaheliotropic plane. 



It was necessary to convince myself that plants indoors placed 

 close to a window receive enough light to cause the leaves to be 

 approximately at right angles to the incident light. 

 Eocperiment 1 . — 



Table I. 



1 1 



Date. Leaf i. Leaf ii. 



March 27, 9.20 a.m 



March 28, 2.30 p.ji 



March 30 



Lamina 



+ 15t 

 +30 

 - 6 

 -30 



Lamina 

 o 

 +15 

 +20 

 +50 

 +40 







A plant whose leaves i. and ii. were both 15° above the horizon 

 was placed, March 27th, so that the underside of i. was towards the 

 light; its position was close to a window, so that the illumination 

 was oblique from above. It will be seen that i. ultimately curved 

 downwards and ii. upwards, the movement in both cases being 

 such as to improve the illumination— that is, to make the leaves 

 more nearly at right angles to the light. 



Experiment 2.— April 17th, 4 p.m. A plant, whose leaves were 

 pressing cpinastically against the ground, was dug up ; and on 

 heing freed from the resistance of the soil, the leaves, as is usually 

 the case, sprung back so as to point vertically downwards J. The 

 plant was then fixed on the klinostat in the " zenith position " (see 

 p. 427); so that the leaves pointed directly away from the light §. 



* The fact of the leaves of R. Ficaria being apogeotropic in the dark, which 

 Frank mentions (p. 46), I also confirmed. The rising of the leaves occurs long 

 before the leaves are etiolated ; so that the experiment is not open to the objec- 

 tion that the plant was in too abnormal circumstances. 



t + means in front of the transverse plane, which in this case is equivalent 

 to above the horizon. 



X R. Ficaria exhibits this movement in the same way as Pinguicvla, 

 Plantago, &c. 



§ It should be noted that when the plant is in the zenith position, as in 

 this case, the transverse plane coincides with the diaheliotropic plane, so that 

 ±<F means at right angles to the light. 



