64 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



(2) the seedling, or later the adult itself, may die or be destroyed; 



(3) the individual may persist without reproducing, a frequent event 

 under keen competition; or (4) normal reproduction may occur, asso- 

 ciated in most perennial herbs with propagation. Ecesis, properly 

 speaking, occurs only in the last instance. It regularly involves an 

 expression of the complete life history, though under the influence of 

 marked adjustment this may be modified in details (Fig. 14). 



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Fig. \^..— Oenothera caespitosa establishing itself in the sun-baked clay of the 

 Bad Lands; The Great Wall, South Dakota. (Photo by Edith Clements.) 



As already emphasized, migration becomes effective only when fol- 

 lowed by ecesis. The latter has usually been regarded as a natural if 

 not regular sequel to movement, but experimental studies have shown 

 it to be altogether exceptional (Clements and Weaver, 1924) . This 

 conclusion is reinforced by the slow changes in composition shown by 

 the plant matrix, in spite of the enormous seed production of many 

 species. Not only must the seeds meet the vicissitudes of transport 

 and of germination, but the highly susceptible seedlings must run the 

 gauntlet of untoward conditions, of destructive coactions, and of un- 

 favorable competition. The final survival represents but the merest 



