CONDITIONS OF EXISTENCE 



35 



chlorophyll bodies of green algae continue to work at 600 atmos- 

 pheres and cress seeds have germinated after an exposure to 1000 

 atmospheres. 



Table V shows the conditions and distribution of Ufe in Lake 

 Michigan. The greatest pressure is 27 atmospheres which on 

 the basis of the work of Regnard would seem trivial. Animals 

 may react to pressure differences but this is not known as no pres- 

 sure gradient can be estabhshed without involving gravity also. 

 Pressure would appear to play a relatively insignificant role. 



TABLE V 

 Conditions in Lake Michigan 



With a rise of temperature both the density and viscosity of 

 water decrease. This tends to cause such organisms as behave 

 like small inanimate particles to sink. Ostwald suggested that 

 these differences are responsible for the depth migrations of 

 plankton organisms. He considered that a decrease in viscosity 



