MOVEMENTS OF THE PARTS OF PLANTS. 545 



GeraniacefR, and the bursting of the hardened endocarp, as in the 

 Almond in the Phanerogamia. 



The causes are owing, Istly, to the universal property of vege- 

 table membrane to contract when in the act of drying up, and that 

 the more so if their chemical nature is the same, the thinner the 

 membrane ; and if it is composed of different substances, the more 

 so, the more they approximate in their quality to jelly; 2dly, 

 the elasticity (however slight) of the vegetable membrane, which, 

 when filled by fluids, is in a state of tension, and which again con- 

 tracts when these fluids withdraw themselves ; 3dly, to the con- 

 traction of a thin- walled cell filled with fluids, which, when the fluid 

 escapes, is either not at all, or only imperfectly filled with air. 

 These causes produce the movements enumerated, the different 

 structure and nature of the cells in the same part of the plant 

 causing an unequal contraction and, with it, a twisting or turning. 



Although the phenomena here enumerated are generally known, I 

 cannot find anywhere a more accurate analysis of the facts that they 

 are based upon. Indeed, this could not be expected when such per- 

 fectly erroneous views of the nature of the vegetable membrane are 

 adopted, as those of Link and Meyen. 



The fact is well known, that vegetable membrane (and, in consequence, 

 also the elongated cells, called vegetable fibres) extends when in a moist 

 state, and contracts when in a dry state. Link has asserted the reverse 

 of this (Elem. Phil. Bot., vol. i. p. 360), and Meyen (Physiologic, vol. i. 

 p. 30.) has invented for it a singular theoretical explanation. I have 

 contradicted this erroneous assertion (Wiegmann's Archiv, 1839, vol. i. 

 p. 274.). Skulls are separated in anatomical researches by filling them 

 with dry pease and putting water into them ; rocks are burst by wooden 

 wedges that are moistened ; if we let fall a drop of water upon paper, it 

 will form a vesicular elevation ; the same takes place on thin boards : and 

 numerous other similar well-known facts might be enumerated. Vege- 

 table substances have frequently been used for hygrometers; for instance, 

 Balance's strips of paper, Hautefeuille's, Tauber's, Ferguson's, Comers', 

 Anderson's, and Franklin's strips of wood, which exhibit, by the amount 

 of their extension, the amount of humidity of the atmosphere. John 

 Leslie constructed a hygrometer of boxwood, similar to Deluc's ivory 

 hygrometer, the former being distended, when wetted, twice as much as 

 ivory (Gehler's Worterbueh, art. Hygrometrie). Others have used 

 other vegetable substances, for instance, strips of fuci, for hygrometers. 

 In answer to my observations, Link says (Wiegmann's Archiv, 1841, 

 vol. ii. p. 407.), " Through disputes that were once carried on between 

 DeLuc and Saussure respecting the hygrometer, it has been proved that 

 dry vegetable fibre contracts by moisture, whilst animal fibre is elongated 

 by it." This statement is altogether untrue, because the question of any 

 material difference between the animal and vegetable fibre was never 

 raised in the discussions of DeLuc and Saussure. But even had this 

 assertion been made by one of them, it could from well-known facts be 

 proved to be a decided error. Link seems to know nothing of the matter 

 but by hearsay, for the result, especially of DeLuc's investigations, was 

 clearly that no difference takes place in this respect between the animal 

 and vegetable parts, excepting a quantitative one. DeLuc, in his Treatise 



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