564 CORRELATION OF DISTRIBUTIONAL FEATURES. 



to an annual plant which uses only a portion of the season in any part 

 of its range. There is also a close correspondence between the dis- 

 tributional limit of Daucus and the line for a daily mean temperature 

 of 40° for the coldest 14 days of the year, but here again there is 

 obviously no significance for this plant in the temperatures that super- 

 vene while the entire race is represented only by seeds. There is 

 nevertheless a parallehsm between the different phases of any climatic 

 condition, as has been remarked before, and this may well mean that 

 there are other indices of temperature conditions critical for Daucus 

 which have not been elaborated in our work, and the isotherms for 

 these may be parallel to the ones mentioned above. It may also be 

 true that there is an unsuspected importance for this plant in the 

 length of the total frostless season and in the low temperatures of 

 winter. 



Spermolepis echinatus and Parietaria dehilis have ranges which are 

 similar to that of Daucus, although not so extended either to the 

 northwest or the east. These plants are also annuals which have 

 different seasonal habits in the different sections of their areas, and the 

 remarks made ahovit Daucus will apply also to their relation to climatic 

 conditions. 



Oxybaphus florihundus (fig. 70).— This herbaceous root-perennial 

 ranges throughout the central United States between the Deciduous 

 Forest region and the Rocky Mountains and north of central Texas. 

 It encounters the entire amplitude for the country, of cold days, and 

 relatively wide ampUtudes of the other conditions, both of temperature 

 and moisture. The narrowest amphtude is that of the moisture ratio 

 (ir/E), which ranges from 0.25 to 0.89. 



TtMKIUruKC 



Oats in Noomal rROTicka St«soN (F. S.) 



Hot D*v*, F. S. 



CoiD Days, F. 8. 



PHrBn>LO«iCiU. Summation, F. S. 



Normal Daily Mcan, coldcst 14 days or Year 



Normal Daily Mcan, Viar 



Prccipitation 

 Normal Daily Mcan. F. S. 

 Days in lonocst Normal Rainy Period, F. S. 

 Days in lonocst Nsrmal Dry Pcriod, F. S. 

 Mean Total, Ycar 



evaroration 

 Daily Mcan, 1887-3, F. 8. 



MOISTURC Rati«s 

 Normal p/e, F. S. 

 Normal ir/Z, F. S. 

 Normal P/t, Ycar 



Humidity 

 Normal Mean, F. S. 



suhshinc 

 Normal Daily Duration, F. S. 



MoisturcTcmperaturc iNOices 



NOMMAL p/e X T, F. S., PMYpiOLOOICAL METHOD CI 



Fig. 70. Climatic extremes for Oxybaphus floribundus. 



