BOOKS AND CURRENT LITERATURE 



The Cause of Growth in Plants. — -Osmotic pressure phenomena 

 have been somewhat universally accepted as the means by which water 

 enters the plant cell and brings about the elongation phase of growth, but 

 Borowikow and others have found this theory seriously inadequate to 

 account for exceptions which have appeared in the experimental results 

 of various workers. Notable among these exceptions are: (1) the 

 fact that the rate of growth frequently bears no relation to the amount 

 of osmotic pressure of a solution in which the plants are growing; and 

 (2) that a rapid growth is not always accompanied by a high osmotic 

 pressure of the growing tissues. 



These exceptions have caused M. Fischer and a few others to attack 

 the problem of the cause of growiih in animal tissues from a different 

 standpoint, and Borowikow has extended the work to the growth of 

 plants by measurements of the growth rate of Helianthus annuus. 

 His results have appeared in two papers,^ in the first of which he de- 

 scribes an analogy existing between the growth rate and the hydration 

 of colloids, which may perhaps be best shown by the following. 



Swelling of Colloids 



1. The rate of swelling of colloids 

 in the presence of osmotically equal 

 solutions is different for different so- 

 lutes. 



2. Swelling is greater in the pres- 

 ence of acids than in pure water. 



3. The swelling maximum depends 

 upon the combined action of both 

 ions of the solute. 



4. The degree of increase of sw^ell- 

 ing caused bj^ certain acids is repre- 

 sented by the following order: 



HC1> HN03> CH3C00H> H2SO4 



Growth of Helianthus 



1. Unlike growth rates occur in 

 osmotically equal solutions. 



2. Acids increase growth rate over 

 the rate in pure water. 



3. The amount of increase of growth 

 in acid solutions depends "upon the 

 combined action of both ions of the 

 acid. 



4. The amount of increase in growth 

 due to the presence of certain acids 

 is represented by the following order: 



HC1>H2 S04>HN03>CH3 COOH 



■ Borowikow, G. A., Uber die Ursachen des Wachstums der Pflanzen. Bio- 

 chem. Zeit. 48, 230-246; 50, 119-128. 1912. 



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