DISTRIBUTIONAL PATTERNS OF VERTEBRATES 447 



tribution. They are taken, instead, to indicate a Wisconsin or 

 post-Wisconsin distribution that could have connected the Mexican 

 and eastern populations of sugar maples. 



The bald cypress {Taxodium distichum) occurs as far west in 

 Texas as the Devil's River (Sargent, 1922). Isolated palmetto 

 (Sabal minor) plants are found on the Edwards Plateau west of 

 Austin, Texas. One of these was found on the floodplain of Bear 

 Creek, Hays County, when we went to in\'estigate the locality at 

 which an isolated specimen of Microhyla carolinensis had been 

 collected far west of the continuous range of this eastern species of 

 frog. The loblolly pine {Pinus taeda) grows on sandy soil over an 

 extensive disjunct area in Bastrop County, Texas. A disjunct 

 population of the greenfrog {Rana clamitans) lives along Alum Creek 

 in this same area. A western montane species, the pinon pine {Pinus 

 ediilis) has disjunct growths as far eastward as Kerr County on the 

 Edwards Plateau. 



The piiion mouse {Peromyscus nasutus), which is distributed in 

 the pinon belt and above in the southern Rocky Mountain chain, 

 is represented by a disjunct sibling species {P. comanche) in the 

 cedar {Jiiniperus) forests of the Palo Duro Canyon and other 

 canyons along the escarpment of the High Plains in the Texas pan- 

 handle. The two are separated today by more than 100 miles of arid 

 grassland (Blair, 1943). The brush mouse {Peromyscus boylei), 

 which is associated with montane forests in the west, has relictual 

 populations (Fig. 5) much farther east than the preceding species. 

 The most eastern of these is in the Ozarks and Ouachita Mountains 

 of Oklahoma, Arkansas, and Missouri and is so little differentiated 

 that it has been treated as the same subspecies as in western Texas, 

 An eastern forest species that shows relictual populations deep 

 into the present grasslands is the pine vole {Pitymys pinetorum) 

 which has a close relative {P. quasialer) in eastern Mexico. The map 

 of the distribution of these voles drawn by Martin and Harrell 

 (1957) gives an erroneous impression of the relation of the eastern 

 species to the grasslands, because the range of this species is drawn 

 to include these relicts. Actually (Fig. 6), the westward distribution 

 of the main body of the population of this species ends at or inside 

 the border of the eastern forest in eastern Texas and Oklahoma. The 

 relictual populations near Kerrville on the Edwards Plateau of Texas 

 (Bryant, 1941) and in the Wichita Mountains, Oklahoma (Blair, 



