CORRELATION OF DISTRIBUTIONAL FEATURES. 561 



The area of Arceuthobium is therefore closely similar to that of Pinus 

 contorta, with the exception of its absence from the northern Pacific 

 coast. The area of the mistletoe (plate 29) has been drawn in a more 

 generalized manner than has that of Pinus contorta (plate 16), because 

 less information is available regarding the occurrence of the former. 



The climatic extremes for Arceuthobium are very similar to those for 

 Pinus contorta, except with respect to the high conditions of precipita- 

 tion, moisture ratios, and humidity encountered by the host in the 

 Pacific-coast part of its range. This is a case in which a sap parasite 

 is not able to accompany its host throughout the entire range of the 

 latter, apparently as a result of the operation of limiting climatic con- 

 ditions upon the parasite. The well-known xerophytic character of 

 the mistletoes apparently brings their distributional behavior into 

 accordance with that of other xerophytic plants in their inability to 

 invade regions of high moisture conditions. The only mistletoe that is 

 found in Washington west of the Cascade Mountains is a locally abun- 

 dant form of Arceuthobium douglasii growing on Tsuga heterophylla. 



TlMKM*TUIte 



Oats in Na*M*L Fnotntmu Sc*«on (F. S.) ■ 



Hot D*v«. F. S. ■ 



Colo D*t«. F. S. C 



PMVsiOLOcicat. SuMiH-noN, F. S. C 

 Normal Dailt HtiM, coldcst 14 oat* or Vcaii C 



Normal Dailit Mean. VtAR C 



PnCCfPtTATION 



Normal Dailv Mean. F. S. ■ 



Oats in lonccst Normal Raint Pcrio^, F. S. ■ 



Oats in lonocst Normal Dry PCR190.' F. S. CI 



'Mean Total, Year Q 



cvaroration 



Dmlt Mean, 1867.8. F. S. Q 



MoIsTURE Ratios 



Normal p/e, F. S. ■ 



Normal n/Z, F. S. B 



Normal P/E, Vear d 



humiditt 



Normal Mean. F. S. ■ 



Sunshine 



Normal Dailt Duration, F. S. ■ 



Moisture-Temrcrature Indices 

 Normal P/E x T. F. S.. Phtsiolocical Method ■ 



Fig. 67. Climatic extremes for Arceuthobium americanum 



Phoradendron flavescens (fig. 68). — ^A remarkably wide range is 

 exhibited by this plant and its varieties, extending from coastal Oregon, 

 through California and the extreme southwest, to Texas, Florida, 

 Indiana, and New Jersey. The species itself is found from New Jersey 

 to Louisiana, variety orbiculatum in Arkansas, Oklahoma, and Texas, 

 variety pubescens in Texas, variety macrophyllum in Arizona, and 

 variety villosum in California and Oregon. 



Both the species and the varieties of this mistletoe are found on a 

 number of different host trees, so there is no such restriction of its 

 range as that shown for Arceuthobium americanum. Little is known 



