OEIGIN EANGE OF SPECIES 15 



extends around the earth in the warmer zones, reaching well toward the 

 limits of the cool-temperate latitudes in both hemispheres. Increasing 

 knowledge of its forms has gradually led not only to the segregation of as 

 markedly different genera as Viscum and Plioradendron, Loranthus and 

 Psittacanthus, etc., but to recognition that nearly all of the genera are 

 exclusively either of the New World or of the Old World the most 

 marked exception being the small and simple genus Arceuthobium or 

 Razoumofskya, with American, European and Asiatic species. 



These facts point to anything but a recent migration of American 

 and European stocks from the original center of distribution; at the 

 same time they do not point to a very ancient origin for our own genera. 

 Perhaps because of their very common occurrence in upland regions 

 though P. flavescens, for instance, may be found in the greatest abun- 

 dance on trees in swamps or river bottoms and even more because of 

 their generally fleshy substance with relatively little lignification, our 

 mistletoes have scarcely left fossil remains, one Tertiary species, only, 

 P. fosstte of Ecuador, being recorded as thus far recognized in the genus 

 Phoradendron. Everything considered, the genus may be regarded as 

 probably of late Tertiary origin in the New World. When and where 

 on this continent its two primary subdivisions came into existence will 

 make a fascinating subject for future study. 



RANGE OF SPECIES 



In the geographic distribution of its species, Plioradendron is rather 

 unusually instructive. The genus is strictly American and extends from 

 Washington, Southern Colorado, the mouth of the Ohio River and South- 

 ern New Jersey to the mouth of the La Plata on the continent, and 

 through the entire West Indian chain : one species occurs in the Pacific 

 island Guadalupe, and two are found in the Galapagos group of Pacific 

 islands both oceanic but with American floras. None of its many spe- 

 cies of fairly homogeneous character possesses a very wide geographic 

 range. Marked examples of wide-spread occurrence are afforded only 

 by such polymorphous species as what is usually called P. latifolium, or 

 an assemblage of intricately related if differentiable species like that 

 usually known as P. rubrum or P. quadrangular e, which range from 

 Brazil to Central Mexico and well through the West Indies. Few spe- 

 cies, indeed, equal in absolute range our native P. flavescens, which occurs 

 from southern New Jersey to the lower Wabash, Oklahoma and eastern 

 Texas, reaching southeast to the gulf and ocean. 



Admirably endowed with mea,ns of free dissemination through their 

 berries with extremely viscid pulp, which leads to their dispersal by 

 birds, these mistletoes seem limited nevertheless to a surprising extent by 



