io8 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



The difference in behaviour between the two, when dead, indicates 

 the existence of a certain amount of differentiation between the plasma and 

 the membrane which encloses it, and the fact, that by sudden plasmolysis 

 the vacuolar membrane may be actually separated, points in the same 

 direction. Moreover, the thinnest plasmattc films, such as surround the 

 distended vacuoles formed by isolated fragments of plasma (see Fig. 6), 

 retain their original diosmotic properties. 



It has also been indicated (Sect. 16) that the existence of a plasmatic 

 membrane does not necessitate any special structure in the central plasma, 

 vacuolar or otherwise. In every case, we ultimately require to determine 

 what are the paths along which a substance diffuses through the plasma, 

 and whether penetration is possible in the case of certain plasmatic 

 organs or elemental units l . Unfortunately, structural appearances seen 

 under the microscope afford no conclusive evidence as to the diosmotic 



properties of the parts examined. The ultimate 

 structure must, however, in all cases, whether a 

 plasmatic membrane be present or not. be such as 

 to afford an explanation of all the facts brought to 

 light by experiment. The fact that the diosmotic 

 properties of the vacuolar membrane are preserved, 

 however rapidly it may be increasing in surface 

 area, proves that it never becomes discontinuous. 

 This fact, however, forms no argument against the 

 existence of a plasmatic membrane, for in artificial 

 precipitation-membranes continuity is maintained, 

 even when growth is extremely rapid. 



All the evidence goes to show that the 

 internal masses of plasma, when necessary, can 

 take on in any exposed peripheral layer the function and character of 

 a plasmatic limiting membrane. The latter hence is not, as de Vries 

 and his pupils concluded on insufficient grounds, an organ, which, like 

 the nucleus, can only be derived from its own kind 2 . Every mass of 

 watery fluid present in the protoplasm must be surrounded by a vacuolar 

 membrane to form a larger or smaller vacuole, while masses of plasma 

 which have escaped from the cell, also become clothed by a plasmatic 

 membrane, and form large vacuolar bubbles in water, but not in plasmolysing 

 solutions. From what has just been said above, it follows that a plas- 

 matic membrane must be immediately formed on the freshly exposed surface 

 as it comes into contact, not with plasma, but with other media, and 



FIG. 6. The formation of va- 

 cuoles in fragments of plasma 

 immersed in water, \\hich have 

 been forced by pressure from a 

 young root hair of Hydrocharis 

 morsus-ranae (X45O). 



1 See Biitschli, Unters. iiber mikroskop. Schaume, 1892, p. 150. 



J Pfeffer, 1890, I.e., p. 224; Klebs, Hot. Zeilung, 1890, p. 550, and 1891, p. 343; Biitschli, 1. c. 

 (Mikr. Schaume), 1892, p. 146, and the literature here cited ; also Sect. 8 of this book. 



