VITAL PHENOMENA 101 



be used to do the work of restoring the turgor, but new osmotic 

 substances must be produced by the cell. According to van 

 Rysselberghe (1899) some plant cells may increase their osmotic 

 pressure by transforming starch into oxalic acid, but his evidence 

 for this is probably slight. 



Pfeffer extended these observations to the pulvinus of the 

 sensitive plant leaf. His observations have been confirmed re- 

 cently by Lepeschkin (1908), who showed that the osmotic 

 pressure of these cells was decreased when they were stimulated 

 and that not only water, but also dissolved substances, diffused 

 out of them. Waller (1904) showed that increased electrical 

 conductivity followed stimulation. 



The cells of the sensitive plants are not alone in their changes 

 in permeability. Lepeschkin (1908) and Trondle (1910) found 

 that light increases the permeability of plant cells to salts and 

 in a lesser degree to dextrose. Fluri (1909) observed that the 

 salts of aluminum, yttrium and lanthanum increased the perme- 

 ability of plant cells to salts and to sugars. After washing out 

 the reagent the cells returned to their normal condition. If 

 Spirogyra were treated with one of these salts, the tannin dif- 

 fused out of it so that if it were placed in a solution of chinin, 

 no precipitate of this alkaloid and the tannin was formed inside 

 the cells. Fluri interprets these results differently, however, 

 owing to the fact that the viscosity of the protoplasm is increased 

 so that the chromatophores cannot be precipitated with the 

 centrifuge. 



De Vries showed that nitric acid increases the permeability 

 of Tradescantia cells to KNO a . In experiments with acids it is 

 necessary to distinguish three conditions : First, the cells may 

 be permeable to the acid, as in case of fatty acids. Second, the 

 permeability of the cell may be reversibly changed by the acid, 

 as in case of mild treatment with fatty acids. Third, the cell 

 may be killed by the acid and its permeability irreversibly in- 

 creased, as in case of the mineral acids. In this experiment of 

 de Vries the cells were probably killed by the acid. 



It was shown by Pfeffer that the anthocyan in plant cells may 

 be used as an indicator to show the penetration of acid. The 

 penetration of acid into the cells of the red beet, red cabbage 

 and red nectar glands of Vicia faba has been observed (Mc- 



