OSMOTIC PRESSURE IN RELATION TO PLANT DISTRIBUTION 185 



In a general way it may be said that increase of osmotic 

 pressure lessens the rate of growth of cells and the rate 

 of regeneration of lost organs in the lower animals. Loeb 

 has found that the effect of a hypertonic solution may be 

 such as to prevent the division of a cell while permitting 

 the mitotic division of the nucleus. Furthermore, ex- 

 posure for a short period to a hypertonic solution forms an 

 essential part of one of Loeb's methods for bringing about 

 artificial parthenogenesis. 



Another interesting result obtained by Loeb is that the 

 larvae of certain Copepods are negatively phototropic above 

 25, but react positively below 10. The addition of 

 sodium chloride to the sea-water in which they are living 

 has, however, the result of causing them to react positively, 

 whereas dilution with distilled water has the opposite 

 effect. These phenomena all appear to be related to the 

 withdrawal of water from the protoplasm, with consequent 

 changes in its viscosity and in the concentration of the 

 reacting substances within it. The subject is one of great 

 interest, and to deal with it superficially would be mis- 

 leading. It has been discussed in detail in the books by 

 Loeb and by Livingston referred to previously. 



