THE MOLECULAR FORCES IN PLANTS. 145 



tube is finally fused up at b. The cane-sugar attracts considerable 

 quantities of water by osmosis. A pressure is thus developed in 

 the apparatus which causes the mercury to rise in the manometer. 

 I found, e.g., in one experiment that at the end of three days the 

 mercury was 47 cm. higher in one limb of the manometer than in 

 the other. The pressure in the apparatus amounted therefore to 

 considerably more than half an atmosphere. 2 



1 See Detnaer, Beitmge zur Theorie des Wurzeldrucks, in Preyer's Sammlung 

 physiologischer Abhandlungen, Bd. 1, Heft 8, p. 29, Jena, 1877. 



2 For further information, see Pfeffer, Osmotisehe Untersuchungen, 1877. 



58. The Diosmotic Properties of the Cell-wall and of the 

 Protoplasm. 



An excellent object in which to study the diosmotic properties 

 of the cell-wall and of the hyaloplasm is afforded us in the 

 staminal hairs of Tradescantia. We remove a tuft of the hairs 

 from the filament with the forceps, and find, on submitting them 

 to microscopical examination, that each hair consists of a single 

 row of cells. The cell-wall, the protoplasm, the nucleus, and 

 lastly the beautiful violet-coloured cell-sap are readily observable 

 in each cell (see Fig. 38). 



From the margin of the cover-glass we now run in glycerine, 

 or more or less concentrated solutions of sugar or common salt. 

 These fluids extract water from the cell-sap, and the protoplasm 

 consequently contracts, so that spaces are formed between it and 

 the cell-wall. We have caused the cells to pass from a turgescent 

 into a plasmolytic condition. Our experiment further proves, 

 however, the important fact that the hyaloplasm of the living 

 protoplasm must be impermeable to the pigment dissolved in the 

 cell-sap of the cells, for the colouring matter does not pass through 

 the protoplasm with the water when plasmolysis takes place. 



The effect is quite different if we allow absolute alcohol to act 

 on the staminal hairs of Tradescantia, and thereby kill the cells. 

 The violet cell-sap now passes over into the protoplasm, since the 

 hyaloplasm has become permeable to the colouring matter. The 

 protoplasm, and especially the cell-nucleus, become deeply stained, 

 and the coloured fluid may even pass out of the cells into the sur- 

 rounding medium. It is also very instructive to plasmolyse cells 

 whose cell-sap is uncoloured, e.g. the epidermal cells of the leaves 



P.P. L * 



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