ECOLOGICAL SUCCESSION. 347 



Succession proceeds until conditions are such as to be favorable 

 to organisms which are immune to their own effects upon their 

 own environment. Ecological succession proceeds from all mores 

 types toward the physiological types of organisms which are 

 adjusted to climatic conditions of the area. On the basis of 

 good evidence, which cannot be reviewed here, but which is 

 to be found in the writings of Cowles ('oi 1 , 'oi 2 ; Clements, '05; 

 Gleason, '08, 'ii; Adams, 'o8 l , 'o8 2 ; Whitford, '06) and others, 

 botanists have reached the conclusion that the vegetation and 

 therefore the chief animal habitats of the local conditions are 



SAND RIDGE CLAY BLUFF 



V", A, i Cottonwood Aspen | near 



V, A, 2 Gray pine Cottonwood ) IV, B. 



V, A, 3 f Black oak Hop-Hornbeam >. 



V, B, i"! White oak White oak Iv, B, i 



v. f Red oak Red oak -v 



V, B, 2\ Hickory Hickory YV, B, 2 



[Rana sylvatica Association] 

 BEECH AND SUGAR MAPLE, V, B, 3 

 [Rana sylvatica Association] 

 Tulip Hickory 



Basswood Red oak ' 

 White elm and white ash Bur oak 



, Swamp whiteoak Bass-wood 



Buttonbush Hawthorn 



f Cat-tail and Bulrush Slippery elm and white elm 



I Water lily and Water Mill-foil River maple 



II, C, i Chara Black willow IV, A, I 



POND FLOOD PLAIN 



FIG. 5. Showing convergence of four types of habitats in northern Indiana 

 to the beech and maple forest. Prepared with the assistance and from the writings 

 of Dr. H. C. Cowles. Read from the extremes toward the center. The figures and 

 letters standing outside the names of the trees refer to the communities similarly 

 numbered in the list on pp. 358 and indicates the plants with which they are asso- 

 ciated. The absence of numbers in connection with a number of the plants is due 

 to the incompleteness of the lists in question. 



converging toward a climatic type immune to its own excretory 

 products. This has been called the climatic climax. The dia- 

 gram (Fig. 5) shows some of the striking stages in convergence in 

 northern Indiana. See also diagrams by Gleason ('08, p. 78, 

 and '10, p. 133). 



The principle of convergence, while not generally established 



