MICHIGAN ACADEMY OF SCIENCE. 129 



RAVINES IN THE VICINITY OF ANN ARBOR. 



BY ALFRED DACHXOWSKI. 



(An Abstract.) 



Preliminary to more oxtended work in the field in experimental physi- 

 ologT, the attempt is made to give a brief ecological snmmary of the 

 various ravines in this vicinity. For convenience four phases are em- 

 phasized in ravine processes, corresponding to relatively dominant ecolog- 

 ical factors. They are : 



(1) A locally typical ravine. 



(2) A ravine influenced by man. 



(3) A ravine of arrested development due to caiDtured territory. 



(4) A rejuvenated ravine. 



,The results obtained show that in each ravine the vegetation, though 

 more or less similar, is decidedly influenced by conditions of soil, light, 

 water-content, temperature, etc., as determined by geology, topography, 

 man, the plants themselves, or the combination of these with other 

 agencies. Concrete cases make it obvious that no ecological factor can 

 be cited as exclusively determining the character of the local flora. Many 

 changes in kind and arrangement of vegetation are independent of domi- 

 nant ecological agencies. They are results which arise from the united 

 action of these factors and, in turn reacting upon the conditions present, 

 thus lead to changes in habitat and consequent distribution of plants not 

 to be attributed either to topography alone, water-table, or character of 

 soil. The main stress must be laid on process, i. e., the varying causes 

 actively at work Avhich bring about the modifications in ravine life, if we 

 are to avoid inconsistencies in definite classification of plant societies. 

 But equally important is the fact that such data must be reinterpreted 

 by the physiological condition of the plants growing in the environment. 

 University of Michigan, Botanical Laboratory. 



