Chapter XV 



177 — 



Origin of Vacuoles 



then elongate and anastomose to form a network. So the trans- 

 formation from large vacuoles to a network and the converse 

 transformation are here again observed. It is only a little farther 

 away from the tip of the filament that all the vacuoles fuse to form 

 a vacuolar canal (Mile. Cassaigne). 



A prolonged observation of growing yeast without the aid of 

 vital stains makes it possible to see that 

 the large vacuoles, which appear rather 

 stable, in these fungi are themselves 

 subject to changes in shape. After a 

 period of stability their contours may 

 suddenly become irregular, angular, 

 may vary continually, contracting and 

 dilating and finally come back to a tem- 

 porarily stable form. Often they are 

 seen suddenly to put out long and thin 

 prolongations, which later contract as 

 the vacuole returns to its spherical 

 shape. 



Ultramicroscopic observation of the 

 vacuoles of fungi (in cases where it is 

 possible because of the faintly luminous 

 outlines of these elements) has shown 

 also that their contours often manifest 

 slowly undulating movements. These 

 phenomena seem to be caused here not 

 only, (1) by differences of imbibition 

 between the cytoplasm and the col- 

 loidal contents of the vacuoles and (2) 

 by movements of the cytoplasm, but 

 also by modifications of surface tension. 







6i& 





Fig. 123. — a, Alaria escu- 

 lenta (Laminariales) , b, Bon- 

 nernaisonia asparagoides ( Rho- 

 dophyceae). Globular vacuoles 

 at one end of cell; plasmodes- 

 mic threads connect the cells In 

 the conducting tissue. (After 

 Mangenot) . 



The phenomenon of vacuolar con- I I 



traction:- In addition to these phenom- Jj 



ena of vacuolar fragmentation, there 

 must be cited here another phenomenon 

 of quite a different nature, namely, a 

 particular state of the vacuoles which 

 was first observed by Weber. In the 

 flowers of the Boraginaceae (Symphy- 

 tum tuberosum, Anchusa italica and 

 Mertensia sibirica), this investigator observed that the vacuolar 

 sap of cells is a jelly, capable, under certain conditions, of contract- 

 ing "spontaneously" i.e., quite aside from all plasmolysis. This phe- 

 nomenon has been observed in flowers infiltrated with solutions 

 containing from 1%-0.1% of neutral red. There is then produced 

 a contraction of the colloidal contents of the vacuole whose con- 

 tours are curiously parallel to those of the cell itself. Weber pro- 

 poses to call this phenomenon vacuolar contraction and interprets 

 it as a syneresis, a name given by Graham to the spontaneous con- 



