FREEDOM OF INTERCHANGE OF HOSTS. 23 



Thorn (Crataegus species). 



Roemer's acacia (Acacia roemeriana Scheele). 



Mesquite (Prosopsis juli flora glandulosa (Torr.) Sargent). 



Water locust (Gleditsia aquatica Marsh.). 



Honey locust (Gleditsia triacanthos L.). 



Prickly ash (Xanthoxylum clava-herculis L.). 



China (Melia azedarach L.). 



Wild China (Sapindus marginatus Willd . ) . 



Black gum (Nyssa sylvatica Marsh.). 



Persimmon (Diospyros virginiana L.). 



Water ash (Fraxinus caroliniana Miller). 



Berlandier ash (Fraxinus berlandieriana A. de C). 



To this list must be added the interesting case of a climbing vine 

 (Tecoma radicans (L.) Juss.) as a host plant observed at Bryan, Tex. 



Xo doubt this list might be very much extended by a careful survey 

 throughout the State. 



FREEDOM OF INTERCHANGE OF HOSTS. 



The question arises as to whether parasitism in the mistletoe is in 

 any considerable degree exclusive, i. e., whether by continued growth 

 on a given host species it becomes less capable of infecting a different 

 species. A survey of the field outside of the Phoradendron jlavescens 

 circle shows that this sort of thing is possible, at least within certain 

 limits. Thus there is a group of species brought together under the 

 generic name Arceuthobium, all of them being parasitic exclusively 

 upon coniferous trees, and some of them upon one species exclusively. 

 More to the point is the case of the European mistletoe (Viscum 

 album) and its circle of related forms. Tubeuf a distinguishes three 

 forms: (1) That infecting broad-leaved trees, Laubholz mistel; 

 (2) one which infects fir trees (Abies pectinata and A. cepJialonica), 

 Tannen mistel; and (3) the form parasitic on pines (Pinus sylvestris 

 and P. laricio), Fohren mistel. Tubeuf maintains that none of these 

 three forms is capable of infecting hosts of the others, and has sus- 

 tained his position by abundant observations in the forest and by 

 inoculation experiments. 



It should be noted here that in the case just cited the form which 

 is parasitic upon broad-leaved trees has numerous hosts — twenty-two 

 host species are listed for a single park forest — and that a good deal 

 of freedom of interchange among hosts is possible. It seems likely, 

 therefore, that the central Texas form of mistletoe may be more or 

 less easily established upon all of the hosts (at least in any given 

 district) by seed carried from the mistletoe growing upon any one of 



a C. Tubeuf. Die Mistel (Viscum album) Pflanzenpathologische Wandtafeln no. 1 

 (text), 1906, and more recently in Xatiuwissenschaftliche Zeitschrift fin Land und 

 Forstwirtschaft, no. 5, vol. 7, 1907. 

 166 



