Chapter XII 



— 127 — 



The Vacuoles 



tiated membrane, and are endowed with properties of secretion. 

 It is this membrane to which DE Vries gave the name tonoplast, 

 which he beheved secreted all the substances dissolved in the 

 vacuolar sap. De Vries, moreover, thought that the vacuoles can 

 not in any case form de novo, but are always transmitted by divi- 

 sion from cell to cell, like the nucleus and plastids. In short, 

 DE Vries compared the vacuoles to a sort of liquid plastid to which 

 VAN TiEGHEM gave the name hydroleucites. 



At the time that DE Vries did his work, however, the origin of 

 vacuoles was unknown. All that was known, and had been known 

 for some time, was that several vacuoles appear scattered about in 

 the cytoplasm of cells which are beginning to differentiate; that 

 they enlarge and then coalesce until in mature cells there is only 

 one enormous vacuole occupying 

 the entire cell, pushing the cyto- 

 plasm and the nucleus back to the 

 periphery. Aside from this, noth- 

 ing was known. As a matter of 

 fact, it is generally impossible to 

 distinguish the vacuoles in living 

 embryonic cells. Hence, in the 

 opinion of the earlier botanists, 

 the vacuoles were lacking in these 

 cells and formed de novo in the 

 course of cellular differentiation, 

 as seems to be indicated in figure 

 82, reproduced here from Sachs. 



Went, a student of de Vries, 

 succeeded, however, in revealing 

 in embryonic cells of certain 

 plants, the existence of small 

 vacuoles vv^hich increase in num- 

 bers by fission. This seemed to in- 

 dicate that the vacuoles do not 



arise de novo, but keep their individuality during the course of de- 

 velopment, and consequently seemed to support the thesis of DE 

 Vries. 



This theory, nevertheless, was not based on sufficiently solid 

 facts. It has not, as a matter of fact, been possible to bring out 

 the vacuolar membrane by means of stains and its existence is 

 manifested only by its property of semi-permeability. It is true 

 that there is the phenomenon of isolation of the vacuoles, which 

 obliges us to admit that there exists, at least in mature cells, a 

 semi-permeable membrane about the vacuoles, more resistant than 

 the rest of the cell. Chambers and Hofler who studied this mem- 

 brane during micromanipulation, describe it as a membrane of 

 inappreciable thickness, very cohesive and extensible, formed of a 

 substance non-miscible with water. The significance of the peri- 

 vacuolar layer is still very much disputed. Some observers regard 

 it as a differentiated membrane (Hofler), others as formed by a 



Fig. 82. — Fritillaria imperialis. Devel- 

 opment of vacuoles in the cortical paren- 

 chyma. (After Sachs). 



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