Oiapter XV 



175 



Origin of Vacuoles 



the cell returns to its initial state. This is therefore a phenomenon 

 entirely comparable to that observed during the formation of aleu- 

 rone grains and during the process of plasmolysis. 



akerman's work has shown that this phenomenon consists of 

 a modification in volume of the vacuoles as a consequence of a 

 great deal of water being taken in by the cytoplasm. The result 

 is a fragmentation of the vacuole, caused by swelling of the cyto- 

 plasm, and at the same time an increase in osmotic pressure. This 

 pressure increases by 5 atmospheres. Centrifuging revealed, as 

 has been seen, that, in the stimulated cell, the vacuoles are more 

 dense than the cytoplasm and, conversely, in the unstimulated cell, 

 the cytoplasm is more dense than the vacuole. 



The study of these phenomena has been taken up recently by 

 DuFRENOY, Homes, and Kedrowsky working on Drosera, by QuiN- 



FlG. 121. — Drosera rotundifolia. Glandular cells in the tentacles. 

 Vacuolar system made visible by red pigment in cells, may change from 

 large to small, spherical, filamentous or reticulate vacuoles. A, after 

 DE Vries. B, after HoMes. 



TANILHA and Mangenot in Drosophyllum lusitanicum. These in- 

 vestigations show that it is necessary to differentiate two sorts of 

 physiologically distinct cells in the tentacles of Drosophyllum and 

 of Drosera. First, there are those which, covering the upper sur- 

 face of the tentacles, are secretory. They excrete the complex and 

 viscous liquid which forms a drop at the tip of each tentacle. These 

 cells, when they are not going through a period of digestion, possess 

 a group of small filamentous or granular vacuoles, an arrangement 

 probably having some relation to the loss of water which takes 

 place in the cell (Quintanilha, Dufrenoy, Homes, Mangenot, 

 Kedrowsky). Secondly, there are the cells which compose the 

 lower part of the head and the pedicel. Each of these cells con- 

 tains, except during the periods of digestion, a large fluid vacuole, 

 colored red by anthocyanin. During digestion, this enormous vacuole 

 becomes very finely divided into a large number of small, globular 

 or filamentous elements, colored violet-grey (Dufrenoy, Man- 

 genot). These small filamentous vacuoles are oriented parallel to 



