224 NATUEAL HISTOEY BULLETIN 



Sporobolus cryptandrus (Torr.) Gray. 

 Triplasis purpurea (Walt.) Chapm. 

 Tribulus terrestris L. (Introduced). 



The plants in the last list are not always sufficiently abundant 

 to form a conspicuous part of the flora, and are always more 

 or less freely mingled with species which were formerly widely 

 distributed over all types of prairies. 



A summary of the flora native to the two Iowa sand-dune 

 areas brings out this relationship in a striking manner, as shown 

 in the following: 



Species common to both the sand-dune areas, and also 



occurring on prairie 31 



Species found on the Muscatine sand-dunes and also oc- 

 curring on prairie 134 



Species found on the Harrison county sand-dunes and also 



occurring on prairie 18 



Total number growing on both prairie and sand-dunes. . . . 183 



Of this number 19 species are more frequent on sandy areas 

 than on ordinary dry prairie. 



The species which seem to be restricted to sandy areas in the 

 Iowa sand-dune sections may be grouped as follows : 



Species common to both dune areas 4 



Species found only on the Muscatine dunes 17 



Species found only on the Harrison county dunes 1 



Total number of dune species 22 



It will thus be seen that in our territory only 22 species seem 

 to be restricted to sandy areas and 27 additional species prefer 

 sand but may occur on ordinary prairie, while 163 species are 

 quite likely to occur equally on either sand or ordinary prairie. 



Other sandy areas .show a similar preponderance of typical 

 prairie plants on those surfaces whidi have become more or less 

 stable but where there has been no development of a cementing 

 and binding soil. At Dune Park, Indiana, the writer found 55 

 such species in one day's search, and other sandy areas show 

 the same result. 



Thus Rydberg, in the Flora of the Sand Hills of Nebraska,2i 

 reports a long list of plants from areas representing various 



21 Contributions from the U. S. National Herbarium, Vol. Ill, 1895, pp. 

 133-194. 



