42 



INTRODUCTION TO CYTOLOGY 



results obtained with artificial systems, if rightly construed, cannot fail to 

 contribute to our understanding of cell membranes and their action (see 

 Beutner, 1933). 



Vacuole Membranes. — The character of the tonoplast, or membrane 

 bounding the ordinary sap vacuole, has been the subject of many investi- 

 gations. In 1885 de Vries found that the large central vacuoles of Allium 

 and Spirogyra could be isolated by placing the cells in hypertonic solutions 

 of a potassium salt, and that the semipermeability of their membranes was 

 retained in a measure for some time. Such observations on onion cells 

 have been repeated and extended by Chambers and Hofler (1931), who 

 have isolated the vacuole with a micromanipulator. They find the 

 tonoplast membrane-*^ to be "a highly cohesive and extensible fluid film 

 of unappreciable thickness." It resembles the plasma membrane in being 

 immiscible with water when normal, in not wetting a clean glass micro- 



Fig. 19. — Discharge of the contractile vacuole (Vi) and the accompanying behavior of 

 subsidiary groups of vacuoles (gr. Vi, gr. Vs) in Euplotes. p.p., papilla pulsatoria. mac. 

 macronucleus. {After C. V. Taylor, 1923.) 



needle, and in being wetted by oil and chloroform. A further resemblance 

 is seen in the failure of acid dyes to pass through either membrane when 

 injected into the cytoplasm (Plo^ve, 19316). 



The osmotic properties of vacuoles are important not only in connec- 

 tion with metabolic processes but also in supporting many plant struc- 

 tures through turgor. It is also by virtue of osmotic action that vacuoles 

 may function in subdividing large masses of protoplasm in the sporangia 

 of certain fungi (p. 165), in pollen tube formation (Woycicki, 1926), and 

 doubtless in many other processes. 



The contractile vacuoles of certain lower animals and plants have 

 similar limiting membranes. Such vacuoles periodically absorb water 

 and solutes from the protoplast and then expel them to the exterior. In 

 some cases, as in Paramcecium trichium (Wenrich, 1926), there is evidence 

 that the membrane is a permanent structure which contracts rhythmically 

 to expel fluid received from subsidiary vacuoles. In fixed material the 

 membrane shows a characteristic fibrous structure. In Euplotes, C. V. 

 Taylor (1923a) finds that the primary contractile vacuole, which is 



2^ Chambers and Hofler extend the term "tonoplast" to the vacuole as a whole 

 with its membrane. De Vries applied it to the membrane alone. See also Plowe 

 (1931o). 



