CYTOPLASM AND NUCLEUS 



begins in solutions of about 0-12 to 0-15 normal 

 strength. This salt concentration gives us a 

 gauge for the amount of turgor. De Vries showed 

 that all salts produce the same result at the same 

 concentration in gramm molecules. We call such 

 solutions which have the same osmotic effect 

 Isosmotic Solutions. If we are able to directly 

 measure the osmotic pressure of one isosmotic 

 solution, for instance, of a sugar solution, by an 

 osmometric contrivance, we may transfer this 

 value to the osmotic pressure in the cells. So it was 

 found that the osmotic pressure in cells is equiva- 

 lent to five and more atmospheres, one atmosphere 

 being equivalent to about 0-3 per cent of salt- 

 petre. 



The action of polioplasma on the growth of 

 living cells consequently consists in the production 

 of substances which generate osmotic pressure. 

 We know that only such substances as do not pene- 

 trate the protoplasmatic layer are capable of pro- 

 ducing osmotic effects. It is very little known 

 what substances having that effect are generally 

 produced by plant cells. It is seemingly highly 

 complex acids related to sugar which participate 

 in generating turgor effects in living cells. Intro- 

 ductory to the process of growth a certain amount 

 of turgor pressure is indispensable. We have to 

 assume that by that pressure protoplasm as well 

 as the cell wall is thinned and first stretched, then 

 new particles of cell wall substance are inserted, 

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