THE DIOSMOTIC PROPERTIES OF THE CELL 93 



temperature has caused the death of the plasmatic films which surround 

 the cell-sap, and prevent the pigment substances dissolved in the sap 

 from escaping. The fact that the cell-wall enclosing a living cell is 

 readily permeable, becomes directly manifest when plasmolysis is produced 

 by means of sugar, or saline solutions coloured with indigo-carmine, aniline- 

 blue, or the red sap of cherries or beetroot, for the coloured fluid appears 

 in the space formed between the cell-wall and the contracted protoplast. 

 The fact, that the protoplast has been caused to contract, shows that 

 the plasmolysing substance has penetrated the cell-wall, but cannot pass 

 through the protoplasm, with which it now comes into contact. If no 

 subsequent increase in volume of the protoplast takes place, it follows, 

 that no perceptible amount of the plasmolytically active substance di- 

 osmoses through the plasmatic membranes, for should even small traces of 

 the plasmolysing osmotic substance slowly penetrate through the plasma 

 to the cell- sap, a gradual rise of the internal osmotic pressure would ensue, 

 causing an increase in volume of the contracted protoplast, and ultimately 

 complete removal of plasmolysis. 



As a general rule, substances, which can diosmose through the 

 plasmatic membrane, can also pass through the cell-wall saturated with 

 imbibed water. Hence a substance can often pass through the cell- wall 

 but not through the plasma, whereas one which can diosmose outwardly 

 through the plasma and its membranes, is usully not prevented by the cell- 

 wall from escaping to the exterior. The plasmatic membrane adpressed to 

 the cell-wall, decides whether a substance may penetrate the plasma, and 

 thus together with the vacuolar membrane determines whether penetration 

 to the cell-sap is possible. Further, the plasmatic membranes confer upon 

 the cell the important property of being able to retain dissolved substances, 

 which might otherwise diffuse outwardly and be lost. 



As a matter of fact, and as is shown in the processes of nutrition, 

 numerous substances are absorbed by the protoplast, and many different 

 waste products are excreted, while very large amounts of nutritive substances 

 must be absorbed from relatively extremely dilute solutions to supply the 

 plant with the various mineral constituents it requires. When dealing with 

 processes of such intricate and obscure character, an experimental in- 

 vestigation of the final results may be instituted, but it is only possible to 

 directly follow the process of absorption, when its path or termination is 

 marked by a colouration, precipitation, or some visible reaction. 



In this respect, the behaviour of the cell with regard to certain 

 aniline dyes is especially instructive. These are absorbed by the proto- 

 plast from very dilute solutions and deposited in the cell, in a short 

 time accumulating there to a marked extent l . Here we are dealing 



1 Pfeffer, Unters. n. rl. Hot. Tnst. z. Tubingen, 1886, Bd. II, p. 179. 



