and of certain Liquids on the Surface of Water. 385 



whether on the surface of water or on that of other liquids. A 

 drop of oil of lavender on the surface of liquid acetic acid 

 forms a wonderfully active figure, which I have already noticed 29 , 

 together with the figures of various liquids on the surfaces ot 

 sulphuric acid, cocoa-nut oil, castor-oil, paraffin, spermaceti, 

 white wax, olive-oil, lard, and sulphur, heated, where necessary, 

 so as to render them sufficiently fluid 30 . 



20. In 1837 Dr. Pietro Savi 31 had his attention directed to 

 the following statements by De Candolle 32 with reference to the 

 contractile motions of plants: — "Si l'on place sur Peau des 

 folioles, ou des fragmens de folioles, du Schinus MoMe, on voit 

 Phuile volatile, contenue dans certaines cellules du tissu, s'echap- 

 per, non par un flux continu, mais par des saccades intermit- 

 tentes, qu'on ne peut, ce me semble, rapporter h d'autres causes 

 qu'a quelque contraction des cellules qui renferment ce sue.'" 

 And again at page 287 of the same volume, with reference to 

 the sudden and singular movements of the leafy fragments : — 

 " ces mouvemens sont dus h des jets intermittens d'huile essen- 

 tielle, qui sortent des cellules, frappent Peau, et determinent 

 dans le foliole un mouvement de recul semblable h celui de 

 Fe'olipyle. On voit ici assez clairement un effet vital."" 



Dr. Savi shows, by a microscopical examination of the leaves 

 in question, that no provision is made for the exertion of a con- 

 tractile force, that fragments of the dried leaves move, that 

 the motions are common to leaves of the Terebintacece, Euphor- 

 biacea, Urticaceae } Asclepiadacece, and some others, and that 

 the true explanation of these phenomena (which are physical, 

 not physiological) is to be found in Carradori's attraction of 

 surface, as explained in his memoirs 33 . 



21. In 1838 Morren 34 showed that a leaf of the Schinus 

 Molle, or American pear, placed on water had a jerking motion, 

 while the surface became covered with a film of a sweet-smelling 

 oil. Another plant, the Passiflorafcetida, is furnished with hairs, 

 one of which, plunged into water, discharges a small drop of 

 oil, which, rising to the surface, expands and contracts several 

 times, and then apparently bursts with violence, the smaller 

 portions going through similar changes. These are well-known 

 effects of surface-tension common to several oils and other 

 liquids, as is also an experiment by Zantedeschi 35 , in which a 



29 Phil. Mag. for March 1862. 



30 Phil. Mag. for November 1864. 



31 Mem. Valdarnesi, 1837, vol. ii. p. 117. 



32 Phys. Veget. vol. i. p. 38. 



33 He refers to Mem. delta Soc. Ital. vols, xi., xii., and xv. 



34 Corresp. Mat Mm. et Phys. de M. Quetelet, 1838, vol. x. p. 339. 



35 Given by Lnvini in his Saggio di un Corso di Fisica Elementare 



Phil. Mag. S. 4. Vol. 46. No. 307. Nov. 1873. 2 D 



