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into one. Both the red cedar and the post oak require plenty of 

 sunlight, i. e., they are intolerant of shade. They never give 

 rise to dense woodlands, but always form open, almost park-like 

 groves (fig. 2). In the sunny patches between the trees the 

 herbaceous and shrubby vegetation of the two preceding stages 

 persists almost unaltered, but in shaded spots there begin to 

 appear forms which are characteristic of the subsequent stage in 

 the succession. 



Fig. 2. Pioneer tree stage along crest of West Rock ridge, New Haven. 

 Between the scattered trees {Qucrcus stellata) occur patches of herbaceous vegeta- 

 tion and shrubs. In the foreground is seen Helianthus divaricatus. The shrubs 

 shown are Rktis typhina. 



Further significant changes in the physiognomy of the vege- 

 tation are foreshadowed by the advent of such trees as the 

 chestnut oak (Quercus Prinus) and the pignut {Carya glabra) . 

 These species, like the red cedar and post oak, are relatively 

 xerophytic and on some accounts they should perhaps be classed 

 with them as pioneer trees. But they differ in two im- 

 portant respects, viz., they are slightly tolerant of shade, and 



