562 CORRELATION OF DISTRIBUTIONAL FEATURES. 



regarding the water-supply of sap parasites and the relation between 

 the seasonal conditions of the host and the maintenance of the tran- 

 spiration-stream in the parasite. It is safe to assume, however, that 

 the water-supply for mistletoe is not subject to as sharp nor as pro- 

 nounced fluctuations as that of most autonomous plants rooted in the 

 soil. The influence of precipitation and soil-moisture conditions is 

 exerted very indirectly on the mistletoes, and we may regard them, 

 for the purposes of our investigation, as somewhat analogous to palus- 

 trine plants. 



Phoradendron encounters wide ranges of all temperature conditions, 

 except in regard to the number of cold days. The wide range of mois- 

 ture conditions which it meets is to be anticipated from its independ- 

 ence of these conditions as they affect autonomous plants. The 

 extremely wide ampUtudes of evaporation conditions through which 

 it ranges apparently indicate that it is able to secure supplies of water 

 sufficient for the maintenance of high rates of transpiration. In the 

 most arid parts of its range, however, Phoradendron flavescens var, 

 macrophyllum is found only on trees that occur in relatively moist 

 situations, and not on the small microphyllous trees, in which the 

 maintenance of the transpiration-stream is precarious. 



The temperature condition which appears to be most potent in 

 limiting the range of Phoradendron is the number of cold days. A very 

 small part of its area hes inside the region in which cold days are 

 encountered, and in this part (the Ohio Valley) it reaches the maximum 

 of 44 days for this condition. 



Tn*»t<MTttiit 

 Diiva IN NoKHAi raoarusa Si«*on (F. S.i 

 Hot D*vs. r S. 



coiD D*T*, r. s.' 



^MTSIOLOCICAL SU«M*TION. F. S. CH 



Neniii*!. Dailt M(ah. cocokst 14 DikT* or VcAK I 

 NonitAi. Daily Mcam, Ycak I 



PwccmTATtoM 

 MofvMAL Daily Mcam, F. 8. I 



DATS tN LONGEST NORMAL RAINT PcrIOD. F. S. ^^M 

 DATS IM LONGEST NoDMAL D«Y PERIOD, F. S. dH 



McAN Total, Year I 



Evaporation 

 Daily Mean, 1887-8, F. S. t 



Moisture Ratios 

 Normal p/E, F. S. Oil 



Normal ir/E, F. S. CHi 



Normal P/E. Year ^HI 



Humioitt 

 Normal Mean. F. S. I. 



Sunshine 

 Normal Daily Duration, F. S. I 



Moisture-Temperature Indices 

 Normal P/E a T, F. S., Physiological Mcthob ' " 



Fig. 6S. Climatic extremes for Phoradendron flavescens. 



Daucus pusillus (fig. 69). — This annual herbaceous plant ranges 

 from the coastal region of Washington and Oregon through California 



