142 DAVENPORT ACADEMY OF SCIENCES. 



beech, birch, hemlock, and sugar maple of the north; the south- 

 ern mole and cottontail rabbit meet the northern star-nosed and 

 Brewer's moles and varying hare, and the southern bobwhite, 

 Baltimore oriole, bluebird, catbird, chewink, thrasher and wood 

 thrush live in or near the haunts of the bobolink, solitary vireo, 

 and the hermit and Wilson's thrushes. . . . The northward pro- 

 longations of southern zones do not carry the complete faunas 

 and floras of the areas to which they belong, but lack certain 

 species from the start and become more and more dilute to the 

 northward till it is hard to say where they really end. Their 

 northward boundaries, therefore, must be drawn arbitrarily or 

 must be based upon the presence or absence of particular species 

 rather than the usual association of species. Counting from the 

 north, the Carolinian area is that in which the sassafras, tulip 

 tree, hackberr}^ sycamore, sweet gum, rose magnolia, red bud, 

 persimmon and short-leaf pine first make their appearance, 

 together with the opossum, gray fox, fox squirrel, cardinal bird, 

 Carolina wren, tufted tit, gnatcatcher, summer tanager and yel- 

 low-breasted chat." 



The western part of the upper Austral (Upper Sonoran) is the 

 arid land termination of the Carolinian area. Its eastern bound- 

 ar}' passes almost directly north and south through the center of 

 South Dakota, Nebraska and Kansas. The Lower Austral (Aus- 

 troriparian) occupies the greater part of the Southern States, 

 sending up prolongations into southeastern Missouri, southern 

 Illinois and Indiana, and southeastern Kansas. Its characteristic 

 birds are the mockingbird, painted bunting, prothonotary war- 

 bler, red-cockaded woodpecker, chuck-will' s-widow, and the swal- 

 low-tail and Mississippi kites. 



"Investigations conducted by the Biological Survey have shown 

 that the 7iortJiward distribution of terrestrial animals aiid plants is 

 gover7ied by the sum of the positive temperatures for the entire season 

 of grozi'th and reproduction, and that the southzcard distribution is 

 governed by the mean temperature of a brief period during the hottest 

 part of the year. Transition zone species . . . can not endure a 

 summer temperature the mean of which for the six hottest con- 

 secutive wrecks exceeds 22° C. (71.6 F.), therefore its southern 

 boundary is coincident with the isotherm of 22° C. for the six 

 hottest w'ceks . . . the southern boundary of the Upper Austral 

 zone agrees ver}^ closely with the isotherm of 26° C. (78.8 F.) for 

 the six hottest weeks." 



