BOOKS AND CURRENT LITERATURE 



349 



The final conclusions which are drawn from the two papers rriay be 

 summed up as follows: I. The elongation phase of growth is not caused, 

 primarily, by osmotic pressure, nor even by turgor pressure, because: 

 (1) growth rate does not increase or decrease proportionally to the 

 solution strength of the surrounding liquid, (2) the most rapidly grow- 

 ing seedling is not the most turgescent one, and (3) a seedling when placed 

 under conditions where an increase of osmotic pressure will result at 

 the same time with a decrease of colloidal swelling, shows a lessened 

 growth rate. II. Growth rate is caused by colloidal swelling of the 

 plasma colloids of the cells, because: (1) the elongation phase of growth 

 is possible only under conditions which favor the hj^dration process of 

 the colloids of the cells, and (2) conditions which increase or decrease 

 the hydration process, increase or decrease the growth rate in like 

 manner. — Edith B. Shreve. 



