GENERAL CONSIDERATIONS. 33 



The idea that the vacuolar membvaiio has special properties not 

 possessed by the general })ody of the cytoplasm is l)y no means a new 

 one. De Vries (1885) has shown, >)y treating- living- cells with plasmo- 

 lyzing- agents containing coloring matter, that the vacuole wall is an 

 osmotic meml)rane like the hautschicht. He has also been al)le to 

 isolate the vacuoles from the cj'toplasm without breaking them, show- 

 ing the wall to have some strength and elasticit}^, and that it retains 

 its identity even when not surrounded b}- a viscid cytoplasm. The 

 vacuoles of Spirogt/m were often seen to divide b}^ constriction when 

 treated with a saltpeter solution. By long innuersion in a saltpeter 

 solution followed b}^ eosin the vacuole wall was hardened, so that it 

 would be broken by pressure without collapsing. De Vries concludes 

 that, there is a very strong similarity between vacuole wall and 

 hautschicht. 



Went (1888) holds that all living- plant cells, with the possible 

 exception of bacteria, Cyanophycea?, and spermatozoids, contain 

 vacuoles, which by division furnish all the vacuoles for the succeed- 

 ing generations of cells. In Ai<per(/llh(!< oryz?e he saw both division 

 and fusion of vacuoles. In a cell of Dtinatlion jMiIlttlans he observed 

 nine vacuoles fuse into two large ones. These then fused to form one; 

 but before the constriction left at the point of fusion had disappeared 

 another constriction had begun to form in another part of the same 

 vacuole, -which increased in depth until it had cut the vacuole in two 

 again. Went expresses his belief that the wall of the vacuole plays 

 an active part in this division. In Oladosporium herbarum and in the 

 hairs on the epidermis of Cucurbita pepo he found that the vacuoles 

 divide just before cell division. 



Went concludes that the vacuole wall is an organ of the protoplasm 

 ranking with the nucleus and the chromatophores, originating- l)y the 

 division of a previously existing vacuole, and never forming de novo 

 in the protoplasm. 



Bokorny (1893) treated living cells with a weak caffein solution and 

 found that the vacuole wall was not killed by it, but that it contracted 

 without losing- its rounded outline, precisely as De Vries describes for 

 vacuoles when the cell is treated with a 10 per cent saltpeter solution. 

 Bokorny points out that, as a dilute caffein solution has but verv weak 

 plasmolyzing power, the phenomenon in this case is one of irritability, 

 the caffein solution being the stimulus and the vacuole wall being the 

 receptive part of the cell. A caffein solution as weak as 0.01 per cent 

 will cause the reaction. 



The work of these authors offers very strong evidence that the vac- 

 uolar membrane is at least a differentiated and specialized portion of 

 the protoplasm, differing molecularly from ordinary cytoplasm, and 

 having many properties in common with the plasma-membrane. 

 20844— No. 37—03 3 



