Nichols: The vegetation of Connecticut 247 



rock are smaller in size and are relatively broader and shallower 

 than rock ravines. In consequence, the atmospheric conditions 

 are seldom as favorable as those of rock ravines, and the vegetation 

 rarely equals that of rock ravines in the high degree of mesophytism 

 attained. Soil moisture, as a rule, would seem to be more im- 

 portant here in its effect on vegetation than atmospheric humidity. 

 The boreal tone which characterizes the vegetation of rock ravines 

 is likewise lacking. This would naturally be expected, not only 

 on account of the less congenial environmental relations but also 

 because of the comparative recency with which ravines in glacial 

 deposits have been developed. 



Spring Brooks. — As Cowles* has remarked, ^"springs and 

 spring brooks may be classed with ravine streams, but differ 

 from them in the relative absence of erosion phenomena." They 

 might equally well, if not better, be classed with spring swamps.f 

 with which they are usually associated. Spring brooks are com- 

 mon throughout Connecticut. Perhaps their most familiar floristic 

 feature is the fringe of alders {Alnus rugosa, Almis incana) which 

 almost invariably lines their banks. Aside from these, the brook- 

 side flora may include any of the species elsewhere cited as charac- 

 teristic of spring swamps. 



The Succession of Vegetation during the Development of Ravines 

 in Unconsolidated Rocks. — In his treatment of the plant societies 

 of the Chicago region, Cowlest has described the development of 

 clay ravines and the concomitant sequence of plant associations. 

 The following observations are quoted from this work: "Wher- 

 ever there is an elevated stretch of land adjoining a body of 

 water, such as a lake bluff, one is apt to find excellent examples 

 of the beginning of a ravine. Fig. i [reproduced in this paper as 

 Fig. 4] shows an embryonic ravine of a type which may frequently 

 be seen along the clay bluffs. ... A ravine of this type is essen- 

 tially a desert, so far as plant life is concerned. The exposure to 

 wind and to alternations of temperature and moisture is excessive. 

 The lack of vegetation, however, is due chiefly to the instability 

 of the soil; this instability is particularly great in the case of clay 

 bluffs, where the seepage of water causes extensive landslide action. 



* The physiographic ecology of Chicago and vicinity. Bot. Gaz. 31: 9S. 1901. 

 t See Bull. Torrey Club 42: 192, 19.5. 1915- 

 J Op cil., pp. 86-88. 



