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 life 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 r61e. 



TABLE V 

 Conditions in Lake Michigan 



Approximate physical conditions 



Depth 



Meters Feet 



Vegetation and animals 



Strong wave action 



Limit of sand-moving waves 



Limit of daily temperature fluc- 

 tuations; limit of wave action; 

 beginning of light decrease; 

 pressure about 2j atmospheres 



Pressure 4 atmospheres, light re- 

 duced to 5 



Seasonal temperature fluctua- 

 tions less than i° C; light re- 

 duced to J; pressure sf atmos- 

 pheres 



Light I; pressure 7 atmospheres 



Probably dark as night; pressure 

 II atmospheres; little change 

 in temperature; nearly uniform 

 conditions 



Greatest depth in lake; pressure 

 27 atmospheres 



0-1.5 



25 



39 



54 



70 

 IIS 



274 



o-S 



26 

 82 



128 



177 



230 

 377 



900 



Bottom organisms wanting 

 on sandy shores, abundant 

 on rocky shores 



Organisms abundant 



Lowest record of Chara and 

 Cladophora. Lower limit of 

 Mollusks except Sphasridse 



Scanty filamentous algas 



Lower limit of most shallow 



water animals 

 Nostoc and diatoms 



No bottom plants recorded 

 No plants recorded 



No plants recorded 



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 



