638 SUMMARY OF CURRENT RESEARCHES RELATING TO 



than the rest of the protoplasm, and retaining its normal properties 

 for hours, and even days, after the latter has been killed. This pro- 

 perty indicates a greater density of its substance. The tonoplast is 

 a sharply defined membrane which detaches itself smoothly from the 

 rest of the protoplasm. Application of 10 per cent, nitrate-solution 

 causes normal plasmolysis ; the outer protoplasm loses its tension, and 

 takes the cosin-staining, while the vacuole remains colourless and its 

 tonoplast in a state of tension. In Spirogyra-calls the outer proto- 

 plasm was commonly ruptured, and, by its contraction, partially or 

 entirely expelled the vacuole. The vacuoles contract into a larger 

 or smaller number of free globular vesicles within the stiffened 

 protoplasm-body. 



The tonoplast agrees with the rest of the protoplasm, and 

 especially with the parietal layer, in their most important properties, 

 both in normal physiological functions and in behaviour to 

 plasmolytic and other reagents. It agrees with the parietal layer in 

 being scarcely or not at all permeable, protecting in this way tho 

 enclosed portions of the protoplasts. They both excrete certain 

 definite substances from their surface, whether stored up in the solid 

 condition like cellulose, or dissolved in the cell-sap like organic 

 acids. In certain cases, as in plasmodia, and in the central circulating 

 movement, both act as motile organs. It is possible in some cases to 

 press out the vacuoles through small openings in the stiffened 

 protoplasm around them ; and they then behave like swarmspores. 



When vacuoles are isolated from the surrounding protoplasm, 

 their tonoplasts are from the first permeable for acids and bases, but 

 not for easily diffusible salts like potassium nitrate. But after a 

 vacuole has remained for some days in this solution, it is more or less 

 permeable for sodium chloride and potassium nitrate ; and this is the 

 case to a greater degree if it was treated at first with a dilute solution 

 of any poison. All experiments indicate that after the death of tho 

 outer protoplasm, the tonoplasts do not become suddenly permeable, 

 but only gradually. This increase of permeability depends there- 

 fore on a molecular change, and not on the formation of fissures. 



In a criticism on De Vries's paper, Herr W. Pfeffer * agrees in 

 the main with his conclusions ; and finds a very serviceable staining 

 reagent for the purpose in a O'OOl- 1 002 per cent, solution of methyl- 

 blue. From a mixture of 1 part of methyl-blue and 10,000,000 parts 

 water, the root-hairs of Trianea, Lemna, and Azolla will, in a few 

 days, absorb the pigment as completely as from a concentrated solu- 

 tion. Methyl- violet is absorbed in the same way, without injury to 

 the currents and other vital phenomena of the protoplasm. Nigrosin 

 and anilin-blue, on the other hand, are not taken up in the same way 

 by the living cell. 



Aggregation of Protoplasm in Drosera. f — According to Dr. H. 

 de Vries, the phenomenon described by Darwin as " aggregation of 

 protoplasm " is in reality due to contraction and division of the 



* Bot. Ztg., xliv. (1S86) pp. 114-25. 



t Ibid., pp. 1-11, 17-2(3, 33-43, 57-64 (1 pi.). 



