26 



pears singularly out-of-place above a steep hillside of almost 

 bare sand. 



Just as the conversion from a xerophytic to a mesoph)1;ic as- 

 sociation proceeded from south to north, so is the reversion 

 proceeding in the same direction. At the south end the hillside 

 is already bare to the top, while farther north the erosion has 

 extended but little above the high-water mark. 



The general effect of the vegetation on the river dune, form 

 its beginning on, may be summarized as tending toward stabili- 

 zation, and, as elsewhere also, toward a mesophytic environment. 

 The accompanying physical factors may hasten or retard or 

 even destroy the effect of the vegetation. It is interesting to 

 note that on the crest of the newly destroyed dune the thickets 

 of bunch-grass and sumach of a new cycle of successions have 

 already appeared.* 



*In this popular discussion of the subject no attempt has been made to give 

 full lists of plants, or to correlate the associations and successions mentioned with 

 similar conditions elsewhere. A fuller treatment is now in preparation. The 

 reader who desires further information on the plant successions in sand is referred 

 to the following articles, in which many of the ecological features treated in the 

 present paper are described in detail : 



Cowles, H. C. The ecological relations of the vegetation of the sand dunes of 

 Lake Michigan. Bot. Gaz. 27:95-117, 167-202, 281-308, 361-391. 1899. 



Gleason, H. A. A botanical survej' of the Illinois river vallev sand region. 

 Bull. 111. State Lab. Nat. Hist. 7:149-194. 1907. 



Jennings, O. E. An ecological classification of the vegetation of Cedar Point. 

 Ohio Naturalist 8:291-340. 1908. 



Jennings, O. E. A botanical survey of Presque Isle, Erie County, Pennsylvania. 

 Annals Carnegie Museum 5:289-421, pis. 22-51. 1909. 



