8 COMPENDIUM OF GENERAL BOTANY. 



" Turgor^ ' Sometimes the cell-wall cannot resist the expansive 

 force of the continually expanding primordial utricle, and as a result 

 the wall will rupture, which indeed sometimes happens in nature. 

 If the utricle is not ruptured at the same time, then it may expand 

 to the limit of resistance and finally rupture. 



Let us now suppose an inverse case. Let there be a more highly 

 concentrated solution outside and a relatively more dilute cell-sap 

 within the cell. In this case more fluid passes outward, and as a 

 result the entire cell decreases somewhat in size. Here again be- 

 comes manifest the difference in behavior of the two cell-coverings, 

 the plasmic membrane and the dead membrane (cell-wall). The 

 cell-wall contracts a given amount, corresponding to its previous 

 expansion. If the wall is very delicate and the action of the solu- 

 tion very sudden, it may be thrown into folds and may finally 

 collapse. As a rule the action of the external solution is sufficiently 

 slow and the cell-wall of sufficient thickness to escape such deform- 

 ity, in which case the 'primordial utricle is removed fr'oni the iiiner 

 cell-wall, corresponding to the decrease in volume of its interior. 

 This continues and the space between cell-wall and utricle is filled 

 by the solution from the outside and the inner cell solution. This 

 behavior of the primordial utricle with certain concentrated salt 

 solutions is also shown with certain dilute poisonous liquids, as for 

 example iodine solution, and dilute acids. A longer or shorter ex- 

 posure will kill the cell. The primordial utricle no longer permits 

 all substances in aqueous solution to pass alike. In the case of 

 plasmolvsis this fact becomes known by the great contraction of 

 the primordial utricle, so that it collects as a lump either in the 

 centre or uear one side of the cell. If, conversely, cells filled with 

 cell-sap, as for example those of beet-root, are placed in pure 

 water, for hours no sugar will pass into the surrounding liquid, 

 although the membrane in itself certainly allows sugar to pass. 

 Upon this impermeability of the living utricle to certain substances 

 rests the possibility of producing within the cell a high hydrostatic 

 pressure, amounting at times to ten or more atmospheres.' (Pfef- 

 fer's investigations.) The apparent elective choice which plants 

 show in regard to the appropriation of food-substances does not 



1 Owing to the lack of a corresponding English noun I have retained the 

 original. — Traus. 



* This subject will again be referred to under Water-movements and Tissue- 

 tension. 



