178 UNEQUAL TURGESCENCE. [CH. VII 



(208) Ciesielski's experiment 1 . 



This experiment is of interest in relation to the 

 mechanism of growth-curvatures because it shows that 

 curvatures might conceivably arise through unequal 

 turgescence of the two sides of a plant-member. 



Take a germinating bean with rather a long root, say 

 40 45 mm., and let it lie on the table for a minute 

 or two, so that it may begin to wither. Impale the seed 

 on a pin transversely to the plane of the cotyledons, and 

 fix the pin in a clamp so that the root is horizontal and 

 1 2 mm. above a surface of water. Then gently bend the 

 root downwards till its lower surface and the water meet. 

 In a few minutes the tip of the root will be seen to 

 be rearing itself into the air, which is due to the increased 

 turgescence of the lower surface of the root. 



The same result may be obtained to a still more 

 marked degree if the root is rendered flaccid by immersion 

 in 5 / NaCl solution before being placed in contact with 

 the surface of water. 



(209) Drooping of leaves during a frost 2 . 



In connection with some of the older theories on the 

 mechanism of growth curvature (see exp. 198, p. 167) it is of 

 interest to note that flaccidity may be a cause of curvature. 

 The leaves of the laurel, Prunus laurocerasus, and of the 

 Portugal laurel, P. lusitanica, droop in a striking way 

 during sharp frost. If a branch is brought into a warm 



1 Ciesielski's Breslau Dissertation, 1871, quoted by Sachs (Arbeiten, i. 

 p. 219). See also Sachs, loc. cit. p. 398. 



2 Moll, Archives Neerlandaises, T. xv. p. 13 of separate copy. 



