SUPPLEMENT 7 



P. 11, 1. 44, for capable of swelling in read saturated with 



13, 11. 3-11, for water enters . . . inflowing water read water continues to 

 enter in spite of the counter-pressure exerted by the mercury. Finally, equi- 

 librium is reached when the amount of the inflowing water is equivalent to 

 that which the mercury can press out in the same unit of time. The pressure 

 exerted on the inner surface of the porous pot is spoken of as osmotic pressure, 

 and the height reached by the mercury gives a direct measure of it. The 

 apparatus serves to compute the amount of osmotic pressure, and is hence 

 termed an osmometer. 



11. 19-31, for and if it were . . . supporting clay cell read its volume is 

 thereby increased. The cell-wall is thus elastically stretched, and, in its 

 effort to contract, squeezes some of the water out of the vacuole. In this case, 

 also, an equilibrium is reached in the long run, namely, when the amounts of 

 water entering and passing out are equal. The osmotic pressure, which can 

 be recognized in the case of the osmometer by the height of the column of 

 mercury, is, in the case of the cell, demonstrated by the tension or extension 

 of the cell -wall. If one of the long cells of Nitella be held between the finger 

 and thumb, and pricked with a needle, it is possible to feel the contraction 

 which results from the reduction of the pressure within. In the uninjured cell 

 the protoplasm is pressed firmly against the cell-wall in consequence of this 

 osmotic or turgor pressure ; without such a resistant layer it could not sustain 

 the pressure any more than could the copper-ferrocyanide membrane without 

 the porous pot. 



14, 11. 1-14, for In certain cells . . . takes place read We shall see later, 

 however, that not all cells behave in the same manner as the beetroot cells 

 used in DE VRIES'S experiment. Even the beetroot behaves differently under 

 certain conditions. As a matter of fact, many cells exhibit a perceptible 

 exosmosis not only of sugar, but also of salts, proteid, asparagin, &c. (com- 

 pare p. 9 of Suppl.). 



15, 11. 36-48, for Thirty years ago . . . only to be expected read DE VRIES'S 

 researches (1884) have shown 



1. 49, for specific gravity read dissolved weight 



I. 54, for gram-molecule to the litre read gram -molecular solution 



16, 11. 17-18, for equivalent of o-oi G.M. to the litre read equivalent of 

 a o-oi gram-molecular solution, 



II. 40-2, for their constituent ions . . . molecule does read their con- 

 stituent ions. Thus potassium nitrate dissociates into the kation K + and the 

 anion NO 3 ~. Each free ion has the same osmotic value as the entire molecule. 



11. 49-55, for We have spoken . . . substances in solution read Previously 

 one sought for the cause of osmotic pressure in the attraction existing between 

 the soluble substance and its solvent ; nowadays, another explanation has 

 come to be accepted. Following VAN 'x HOFF, one ascribes to substances in 

 solution 



17, 1. 16, for eel read cell 



1. 18, for sugar read cane sugar 



I. 34, delete of before the pressure 



II. 42-3, for impacts . . . ions read impacts of the molecules and of the 

 ions dissolved in water 



1. 44, after theory insert which indeed is not the only one possible (comp. 

 STEINBRINCK, 1904). 



