ECOLOGICAL SUCCESSION. 63 



1-2. Mixed Pine and Cotton-wood Stage. 



These areas lie on the first ridge from the lake. The sand 

 shows traces of humus which is indicated by a slight darkening. 

 The characteristic grass is the bunch grass (Andropogon scoparius) 

 which occurs in dense bunches much more closely set than 

 Calamovilfa in the preceding. The juniper (Juniperus com- 

 munis), the bear berry and young pines (Pinus Banksiand) are 

 the dominant plants, although old cottonwoods and scattered 

 individuals of all the plants of the preceding stage are present. 

 Two such stages were studied. 



2. Pine Stage. 



The sand here is stable and considerably blackened by humus 

 except in blowouts w r here the wind keeps it constantly shifting. 

 The trees are scattered stunted pines (Pinus Banksiand). The 

 large areas of sand are covered with the recumbent bear berry; 

 scattered specimens of many of the herbaceous plants of the 

 earlier stages are to be found. The New Jersey tea (Ceanothus 

 americamis) and the juniper are among the most characteristic 

 shrubs. The cactus (Opuntia Raffinesqiiii) occurs in the older 

 stages only. Three stations have been studied; two, 2A, and 

 2B (adjoining \A and \B] and iD, at Dune Park, Ind. 



2-3. Mixed Pines and Black Oaks. 



The transition area between pine and oak is characterized 

 by the presence of seedlings of the oak, the choke cherry, the 

 fragrant sumac and an abundance of cacti and Liatris. The 

 ground is much darkened. Herbs are much more numerous 

 than earlier but bare spots of relatively clear sand continue, 

 even after the oaks have entirely displaced the pines. Such 

 transition areas proper have been so much disturbed that only 

 the open bare sandy places in the oak areas are here considered 

 as belonging under this head. 



3. Black Oak Stage. 



We now find the sand to be much darkened by humus and 

 locally covered with a dry moss or with dead leaves. Grasses 

 also partly cover the ground. The shrubby undergrowth is 



