diosmose outwardly in precisely the reverse direction 1 , in order to be 

 removed from the cell. 



The same general relationships hold equally good, whether the 

 diosmotic properties of the plasmatic limiting membranes and of the 

 remaining mass of the plasma are, or are not, constantly of similar 

 character throughout. As a matter of fact, there is no doubt that the 

 osmotic properties of the plasma and its membranes are by no means 

 alike, nor that they may vary from time to time. Mention will be made 

 (Sect. 1 8) of the necessity for the existence of these plasmatic limiting 

 membranes, on both internal and external surfaces of the primordial utricle, 

 and of the manner in which these are preserved and retained however 

 the shape of the protoplast may alter. These physiologically important 

 structures may be termed the plasmatic membranes, the peripheral one, 

 bounding the ectoplasm externally, being called the ectoplasmic membrane, 

 the internal one, bounding the endoplasm internally, being called the 

 endoplasmic or vacuolar 

 membrane 2 . 



In every case, the 

 limiting membranes deter- 

 mine whether or not a 

 given substance shall be 

 absorbed. It may readily 

 be seen that dyes which 

 do not diosmose, penetrate 

 neither the ectoplasmic, nor 

 the vacuolar membrane, as 

 the case may be ; whereas 



FIG. 4. Cells from the radicle of Zea Mais(y.y]$\ (a) in water; 

 *) after plasmolysis in 5 per cent. KNOs ; (c) in 2-3 per cent. 



any substance that passes these, rapidly diffuses throughout the mass of the 

 plasma* and either reaches the cell-sap, or escapes from the cell, according 

 to whether the substance in question was within or without the cell. 



It is true, that the protoplast is not homogeneous, but the above 

 facts and conclusions are reconcilable with the most varied internal 

 structure. For the present it may be left undecided, whether in certain 

 cases diosmosing substances do not actually penetrate the living structural 

 elements of the plasma, and whether the nucleus, chromatophores, &c. 

 may be covered permanently, or temporarily, by a limiting membrane 

 having special diosmotic properties (see Sect. 18). If the space between 

 two diosmotic membranes were filled with glass beads and water, dissolvec 

 substances would pass through the capillary interstices and spaces, without 

 penetrating the glass beads, which correspond in this analogy to the 



' Pfeffer, Landwirth. Jahrb., 1876, Bd..v, p. 113: Osmot. Unters., 1877, p. I 5 .v 

 3 See Pfeffer, Zur Kenntniss cler Plasmahaut u. d. Vacuolen, 1890, p. 188. 



