536 CORRELATION OF DISTRIBUTIONAL FEATURES. 



ward extension of Liriodendron does not carry it far beyond a mean 

 annual rainfall of 40 inches, nor into the region with more than 25 

 days in the longest dry period. 



Bulhilis dactyloides (fig. 45). — The areas of relative abundance for 

 Bulbilis (plate 10) have been charted in an effort to depict the virgin 

 conditions of the distribution of this grass, using all available sources 

 of information, but the resulting map is probably less faithful to the 

 facts than the map of Liriodendron or the map of the relative abun- 

 dance of Pmns tceda. The areas of the latter are unfortunately so small 

 that they frequently comprise no climatic stations whatever, thereby 

 rendering an adequate discussion of them impossible. 



The range of Bulhilis crosses the United States in a broad belt 

 between the ninety-fifth and one hundredth and sixth meridians, 

 extending from the Canadian boundary in North Dakota to southern 

 Texas. In the North the distributional area is narrower than the 

 Grassland, not reaching to its western edge; in the South the distribu- 

 tion is more extended than that of the Grassland, reaching eastward 

 to Louisiana and westward into the Desert-Grassland Transition 

 region. The only limits of the geographical distribution of this species 

 that fall within the United States are the eastern and western ones. 

 The center of ecological distribution extends from South Dakota to 

 northern Texas, and the subcenter of ecological distribution is only 

 from 100 to 200 miles in width, surrounding the center. Both of these 

 areas lie entirely within the United States (see plate 10). 



y TCMPERATURC 



Days in Normal Frostlcss Season (F. S.) I l-^^l%^^— — — — I ■■:■■:■:■^:■:,:,:\■■'/■:<■^■■::■\ 



Hot Days, F. S. I \////// / ///////ZZZZZZm^m'/// // //// //A- ■■ : ■■• ' . '■ '■ ■■ ■ ■'■ ■: . ■■'■I 



Colo W^K^^^^K^^KKtKKtttttMI^K^tl^^^^KKKt^^EZZZMZ 



Physiological Summation, F. S. I [y:\■V/////77mmmar?//////////////yy.■■■■:■:■:■:■:■::■■■.■■.:^ ' 



Normal Daily Mean, coldest 14 days of Year \:-\<<<y.r///// 777777M^^^^^a^^^^K^/////r.-:-: ■.■■■.■■.■■.■■■■■.■■A 



Normal Daily Mean, Year W:::- }■:■:■■:■ 1^— ^1M^^My^/y/V>V>1::-V.C--.->:-:-| 



Precipitation 



Normal Daily Mean, F. S. I l:- ''7Zyl^^^K^^K^ 7//////i::-::-:-:\ 



Days in longest Normal Rainy Period, F. S. Wn7777M^^^^^m77///f///k:-:::-: ■:■:■ .-■.■:■■■•. ■: -•.■•.■•.■•. -.I 



Days in longest Normal Dry Period, F. S. I I:-;-: -.V/ Z^^^^^^KMy. -: ■:■:■:■:■:] 



Mean Total, Year I \:-:v.-/.-.-U7////////i:-\-:-::::-:-:-::-\-:y.-J 



Evaporation 



Daily Mean, 1887-8, F. S. I l:-:-V.--l////// 7:777Z^^W^^rTT?: -' \^■■^■^•.■■.■]■■.■\ •:.■/. M ~ 



Moisture Ratios 

 Normal P/E, F. S. I I ^1 ////i:--: l 



Normal n/E, F. S. dUSI^^M II I 



Normal P/E, Year _ I I-'- ■^^- V//^-:-- | 



'^ Humidity 

 Normal Mean, F. S. I - 



Sunshine 

 Normal Daily Duration, F. S. ^ZZZZZZZW^^^^K^^^^^M I 



Moisture-Temperature Indices 



Normal P/E x T, F. S., Physiological Method I I I ^— — ^ I 



Fig. 45. Climatic extremes for Bulbilis; center of distribution (black), subcenter (shaded), fringe (dotted). 



