i 9 2o] TAYLOR— SUCCESSION OF MOSSES 455 



found in this region; but the maple may herald the coming of the 

 climax forest of beech and maple. Directly east of Wheeling, 

 along the lake shore at Glencoe, the upland forests are dominated 

 by oak, although maple is present in the ravines. 



The Carroll Creek canyon is a narrow valley with high and in 

 many places nearly perpendicular walls of limestone. The stream 

 meanders back and forth across the ravine and frequently washes 

 against the rock wall. All successions, from the first pioneer 

 lichens and liverworts to trees with decidedly mesophytic under- 

 growth, may be found within a short distance of each other. This 

 is by far the best moss habitat which has been included in the 

 present study. Although no evaporation data are available upon 

 this region, it is probable that the excess of humidity over evapo- 

 ration is greater than in the Chicago region proper; while the 

 absence of dust from factories and smokestacks may also be a 

 factor in favor of more luxuriant moss development. 



Plant successions 



All the successions studied may be placed in two general groups, 

 xerarch successions and hydrarch successions. 



Xerarch successions 



Under the xerarch series are included all successions which 

 have developed from or through xerophytic stages even though not 

 xerophytic at the present time. Among the most important of 

 these within the Chicago region are the successions on dune sand. 



Sand dune succession. — The lake beach, while not strictly a 

 dune formation, must necessarily be included in the dune series 

 leading back from the lake. Here the sand is constantly being 

 moved, either by the waves or, when dry, by the wind. Even 

 during the summer the waves frequently wash over a space several 

 rods in width; while in winter the effect of water and ice is felt still 

 farther inland. Very few plants are able to gain a hold under 

 such unfavorable conditions. Occasionally a few annual seed 

 plants can be found; and sometimes upon the upper beach seed- 

 lings of the cottonwood and willows, as well as a few grasses, begin 



