28 MISSOURI BOTANICAL GARDEN. 



In water habitats are encountered such factors as depth, 

 motion, rapidity of running water; attachment surfaces, i e.[ 

 vertical faces of rocks subject to direct force of water; con- 

 cave or protected surfaces under waterfalls where the atmos- 

 phere may be saturated and surfaces moist though plants are 

 not submerged ; soft, smooth, muddy floors of streams from 

 which thalli may be easily swept by variation of currents de- 

 pending on variation in volume of water which fluctuates 

 periodically with rains; rocky, brick or cinder covered beds; 

 the better aeration of water rapidly running over rocky 

 beds ; turbidity of water ; presence or absence of sewage or 



beaten rock surfaces subj 



tendency 



and 



Habitat Characters 



These particular habitat characters are naturall; 

 by the more general meteorological conditions and 

 that the physical characters of a habitat are fairlv 



be able to live under th 

 ay become necessarilv 



minished in that some 



«/ — - ~ ~ |^-.w* A .ix^ n.u xj\J U1UI1UUU" 



lize so large a proportion of light, moisture, space or nutri- 



men 



These 



may 



for existence, hence 



found 



subject to continuous variation. It is evident that physio- 

 logical, physical and biotic factors in the ecological problem 

 are closely related. While physiological factors are of vital 

 importance in the study of associations it will hardly be pos- 

 sible to give them specific consideration though an attempt 

 will be made to note as far as possible the influence of physi- 



Habitats 



diam 



gradually sloping to the edge. The 



