MICHIGAN ACADEMY OF SCIENCE. 117 



to grouping, which otherwise would be limited to and depending upon soil 

 water factor alone, and hence would have been either very limited or else 

 wholly absent. 



Just as striking is the character of the vegetation in a smaller ravine which 

 enters into this one from the west a few feet farther down. Here as else- 

 where the behavior and arrangement of plants varies because of several 

 factors; principally on account of modified relations between humidity and 

 insolation due to the condition of the plants themselves, the reaction of plants 

 in preventing erosion, in binding and enriching the soil. The accumulation 

 of humus in one place, the destruction of it by fire in another; the no less 

 important condition of habitat as determined by the trough-like or the 

 talus-like character of the slopes, north and south exposure, prevailing west- 

 erly direction of rains; characteristic seed dissemination and germination, 

 and the physiological condition of the invading plants — ^these, and more, 

 make it obvious that the analytic treatment, or the explanation on the basis of 

 one or few factors is not sufficient. Not only is it unsatisfactory to studv 

 the habitat as such, i. e., as it presents itself statically at the time of inves- 

 tigation; not even the standpoint of physiographic change and the conse- 

 quent movement of a dependent fauna or flora is adequate to account for 

 the changes and distril^ution of life in this region. A knowledge of the re- 

 actions of plants upon their environment — the functioning between organisms 

 and environment — is equally essential for an interpretation of the hal)itat if 

 dynamically considered. This will not be surprising to any one who ap- 

 proaches the problem from the physiologist's(9) point of view, and recognizes 

 that a fuller account of physiological activities and reactions would clearly 

 include an answer to a more satisfactory understanding of such terms as 

 "habitat," "dynamic/' "process." However, quantitative study, as well 

 as careful and definite analysis of the conditions must be continued for some 

 time in order that the various changes a)id phases may be correlated with 

 the factors in question, and the extent of modification due to them may be 

 recognized. 



Worthy of note is the flora occurring at ground water level. This point 

 is about 250 feet (76 m.) from the margin, and about 30 feet (9 m.) abo^-e 

 the level of the river. During the months of July, August and the early 

 part of September (1904) temperature readings, taken about three o'clock 

 in the afternoon both at ground water level and at a point 65 feet (19 m.) 

 directly above on the upland of the eastern slope, showed an average differ- 

 ence of 5° and 6.5° C., for air and soil temperature respectively. The 

 ]ihysical water content of the soil averages slightly more than that last men- 

 tioned. The more alluvial character of the soil, together with increased hu- 

 midity and the continual presence of flowing water favor a dense luxuriant 

 flood-plain region. The following are a few forms to be found here and in 

 the direction toward the river margin: Jugians nigra, J. cinerea, Tilia ameri- 

 cana, Ulums fulva, V. americana with Carpinus caroliniana, Malus coronaria, 

 Salix discolor, S. lucida, S. nigra, as a tension line nearer .the water, and 

 Prunus americana, Acer saccharum, Cornus candidissima, C. alternifolia, 

 Hamamelis virginiana higher up. The most common associated herliaceous 

 species are: Geum strictum, G. canadense, Sanicula marylandica, Equisetum 

 hyemale, Galium triflorum, Smilax herbacea, Rudbeckia laciniata, Urti- 

 castrum divaricatum, Solidago flexicaulis, Deringa canadensis, Collinsonia 

 canadensis. Campanula americana, Washingtonia claytoni, Parthenocissus 



9. Clements, F. E., Research Methods in Ecology, 1905. 



