560 CORRELATION OF DISTRIBUTIONAL FEATURES. 



Wide ranges are exhibited by Sparganium for both temperature and 

 moisture conditions, due to its extended north-and-south range in the 

 Eastern States, and to its occurrence from the Atlantic coast to the 

 arid interior of Washington. Its climatic extremes are of interest in 

 comparison with those of Sium, which shows the broadest amplitudes 

 of any of the plants that we have selected for investigation. The dis- 

 tribution of Sium indicates that it is able to withstand the entire 

 gamut of temperature conditions for the United States, excepting those 

 encountered in peninsular Florida, and that it is excluded only by the 

 lowest conditions expressed by the moisture ratio (0.40 or lower). 

 Sium, DuUchium, and Sparganium are apparently alike in being unable 

 to withstand the highest intensities of evaporation, in spite of the 

 saturated substrata in which they are invariably found, apparently 

 belonging to that already well-known group of plants in which the 

 transfer of water from absorbing to transpiring organs is internally 

 limited. 



TiMraUTUMt 



D«r« iM NomuL F*o«TL(t« SuaON <r. S.) C 

 Hot D*t«, F. S. I 



Cai.0 D*<r«, F. S. I 



PMTSieioowM. Summation. F. S. (1 



NORMkL DaiLT MCAM, Cai.BIST 14 OATS Of VUM ■ 



NOKMAL Oailt Mcah. Vcaii ■ 



P«eclPtTATIO«l 



Normal 0A4tv Mcan. F. S. Q 



DATS in LONOCST NORMAt RaINT PcrIOD, f. S. ■ 



Dais in lonocst Normal Ort Pirico, F. S. ■ 



Mean Total. Viar I 



Evaporation 



Daily Mean. <e37.8, F. S. |HH 



Moibturc Ratios 



Normal P/E, F. 6. 1 — ^ 



Normal rr/E, F. S. I ■ 



Normal P/E, Vcar I ■ 



Humioitt 



Normal Mean, F. S. I 



Sunshine 



Normal Oailv Duration, F. S. I M 



Moisture-Temperature Indices 

 Normal P/t x T. F. S., Phtsiolocical Method I ■ 



Fig. 66. Climatic extremes for Sparganium americanum. 



Arceuihobium americanum (fig. 67). — This mistletoe is found 

 throughout the Rocky Mountains and the mountains of the Great 

 Basin and its western edge. Its actual occurrence is limited to the 

 forested portions of the area indicated for it in plate 29 (see plate 1). 

 A number of the climatological stations located within the area credited 

 to it are not in situations actually occupied by Arceuthohium, and 

 consequently some of the moisture conditions, in particular, are higher 

 than indicated in figure 67. 



Arceuthohium americanum is chiefly confined to Pinus contorta 

 (including P. murrayana) as a host, but appears to be absent from it 

 in Washington, Oregon, and California east of the Cascade Mountains. 



