ECOLOGICAL SUCCESSION. 351 



plants are arranged irregularly as roughly indicated by the 

 letters in Fig/7.^ After the land is put to agricultural uses, they 

 are arranged as in Fig. 8. Here the plants are all of one kind 

 and are arranged in rows. A grove of the original vegetation is 

 sometimes left, and some of the original plants remain near the 

 fences, etc. 



The fence rows and road sides are usually inhabited in the 

 forested districts, and often also in the prairie by forest margin 

 animals. The weedy, shrubby roadside and fence row is dupli- 



Fig. 10 



FIG. 9. The solid of an ideal curve, representing the distribution of numbers 

 of individuals of a mores with respect to degrees of variation of environic factors 

 in space but without reference to distance or area covered by the degrees of varia- 

 tion. The central or modal portion is the area of ecological optimum. 



FIG. 10. Showing the distribution of the same mores, after the natural vegeta- 

 tion has been supplanted by agricultural plants and the mores has been left in 

 the fence rows, roadsides, ravines, situation which represented the outskirts of 

 its possible range under primeval conditions. 



cated in the abandoned fields which are common on the poorer soils. 

 In a forested area, some forest animals live after the clearing proc- 

 ess is finished, in fence corners, under stones, etc. The dis- 

 tribution of a given species with respect to conditions is repre- 

 sentable as the solid of an ideal curve, Fig. 9, the modal portion 

 of the curve being the optimum conditions for the species in the 

 forest. When the forest is removed, if we assume that the species 

 can still live for a time, we find it in several different situations, 

 which represent the outskirts of the range of toleration. Such 

 places are protected ravines with bushes, fence corners, and 

 partially cleared woodland. None of the situations lies within 



