70 Bulletin 1, Biological Society of Washington, 1918. 



Plain, perhaps for one reason on account of richer accumu- 

 lations of humus. 



We have seen that the potency of ecologic requirements 

 and of historical factors are such that about a third of the 

 entire flora of the Washington area is confined (or nearly 

 so) to one side of the Fall Line or the other. 42 In proceeding 

 from this conclusion to consideration of the part played by 

 the Fall Line in delimiting faunal elements, we must recall 

 not only the great diversity in edaphic conditions between 

 the Piedmont and the Coastal Plain, but also the divergence 

 between the more complete ecologic surroundings of animal 

 life that consist of these conditions added to and modified by 

 vegetation. 



Plants and plant associations have great influence on 

 animal life, and the presence or absence of certain plants is 

 the determining factor in the distribution of numerous ani- 

 mals. This is especially true of insects, various species of 

 which breed exclusively upon single host species. Such 

 forms are frequent among the jumping plant lice (Psyl- 

 lidae), ordinary plant lice (Aphidae), scale insects (Coc- 

 cidae), leaf hoppers (Jassidae), lace bugs (Tingidae), leaf 

 bugs (Miridae), leaf beetles (Chrysomelidae), long-horned 

 beetles (Cerambycidae), weevils (Rhynchophora), and but- 

 terflies and moths (Lepidoptera). 



The influence of the different conditions above and below 

 the fall line, upon another group of insects, the Orthoptera, 

 members of which are not so restricted in feeding habits, 

 as those mentioned, is brought out in a paper by Rehn and 

 Hebard. 43 They record 47 species as pertaining chiefly to 

 the Piedmont, 101 to the Coastal Plain, while only 52 range 

 generally over both areas. 



Ulke lists 44 23 species of beetles of austroriparian and 14 



5 in this connection note R. M. Harper's statement that "The rather 

 vaguely defined 'Austroriparian area' of some botanists — or rather biolo- 

 gists — is practically the coastal plain, and the boundary between that and 

 the 'Carolinian area' is simply the fall-line, the cause of which is purely 

 geological, and not climatic." (Bui. Torrey Botanical Club, 31, No. 1, 

 Jan., 1904, p. 10). 



43 Rehn, J. A. G., and Hebard M. Studies in the Dermaptera and Orthop- 

 tera of the Coastal Plain and Piedmont Region of the Southeastern United 

 States. Proc. Ac. Nat. ScL, Philadelphia. 68, 1916, pp. 87-314, Pis. 12-14. 



*»Proc. U. S. Nat. Mus., 25, 1902, pp. 3-4. 



