Guilliermond - Atkinson — 178 — 



Cytoplasm 



traction of a gel when liquid is expelled. The phenomenon pre- 

 supposes the existence in the vacuole, around the contracted jelly, 

 of a liquid phase (serum) produced at the moment of contraction. 

 This phenomenon of vacuolar contraction seems to be very gen- 

 eral indeed. There is frequently encountered, in the epidermal cells 

 of flowers, a colorless space enclosing a contracted intravacuolar 

 mass and surrounded at the periphery of the cell by a thin cyto- 

 plasmic layer. Neutral red may be superimposed upon the natural 

 color of the vacuolar sap, when it is rich in anthocyanin compounds, 

 and will stain the contracted vacuolar mass intensely. Careful ob- 

 servation of the colorless space reveals that it is not empty. It is 

 occupied by a fluid. Plasmolysis of this modified vacuole, moreover, 



is quite possible and water is lost from the 

 peripheral colorless fluid, which appears at 

 first very poor in dissolved material. Little 

 by little, over a period of from 24-48 hours, 

 however, the fluid reddens. The reddening 

 never reaches the intensity of that of the 

 contracted mass. It is evidence, however, 

 of a slow penetration of colloidal material 

 into the peripheral liquid. Then a second 

 contraction is frequently produced at this 

 time. The fluid separates into a new color- 

 less peripheral serum, and into a deeper red 

 region, contracted about the mass originally 

 isolated. 



Weber thinks that the same phenom- 

 enon may explain the presence in many 

 phanerogam cells of two categories of 

 vacuoles which are adjacent in the cell, the 

 one liquid and lacking in tannin, the other 

 formed of a tannin jelly. These will be 

 taken up later. Weber underlines also the 

 potential importance of this phenomenon in 

 the realization of rapid changes in the 

 turgidity of cells, perhaps in the mechanism of certain organ move- 

 ments. He points out in this regard that the motor swellings of 

 leaves of the Leguminosae (Mimosa), as Mangenot has shown, 

 have vacuoles containing a tannin jelly, side by side with small 

 vacuoles which do not contain colloidal substance. Weber com- 

 pared this vacuolar contraction to the natural production of large 

 colloidal corpuscles observed in the vacuoles of the mature cells. 

 This contraction can not be attributed to a phenomenon of syne- 

 resis, for it consists only in the partial precipitation of the vacuolar 

 colloid. It seems, on the contrary, to correspond, as we have said, 

 to the formation of a coacervate within the vacuolar sap. 



Fig. 124. — A, B, Sac- 

 eharomyces ellipsoideus vi- 

 tally stained with neutral 

 red, vacuoles in buds seem 

 to form de novo. C, D, 

 Oidium lactis, vacuoles in 

 branches seem to form de 

 novo. 



Origin of vacuoles:- P. A. Dangeard and then P. Dangeard, 

 as a result of his own work on aleurone grains^ were led to adhere 

 to the theory of de Vries and Went and to admit that the vacuoles 



