109] NORTH AMERICAN AND WEST INDIAN CUSCUTA—YUNCKER 19 



the study with cavities in them were indicative of galls caused by insects. 

 It was not possible, however, to identify the insects causing the galls. 



Engelmann makes the following statement (1843): "I am now con- 

 vinced that although many Cuscutae prefer some plants to others, yet 

 there is no constancy in this respect, but the same species often grows 

 upon a great variety of widely different plants. I did wrong, therefore, 

 to name them from the genera upon which they grew and I should much 

 prefer to see the names of C. cephalanthi changed into C. tenuifiora, C. 

 coryli into C. incurve, C. saururi into C. umbrosa Beyr.?, C. polygonorum 

 into C. chlorocarpa and Lepidanche compositarum into L. squarrosa if they 

 had not yet been published." Later he actually did make some of the 

 substitutions mentioned. It is a fact that certain species apparently have 

 a preference for certain host plants, but, as Engelman indicates, this is not 

 a constant characteristic. Some species live predominantly, however, on 

 certain classes of plants as, for example C. exaltata which is ordinarily 

 found on trees, while C. salina shows a predilection for saline herbs, and 

 so on. The majority prefer, however, the more succulent herbaceous 

 plants. 



Except for a few species parasitic on economic plants and liable to 

 distribution by artificial means and a few species with a wide variety of 

 forms they seem to be more or less limited in their distribution. There 

 seem to have been originally two points of dispersal in North America. 

 One was apparently somewhere in the eastern part of the United States, 

 probably somewhere along the Appalachian range and the other in the 

 southwestern part of the continent, either in Mexico or the southwestern 

 United States. The species inhabiting the different regions possess group 

 characteristics that are fairly typical of those regions. The species in the 

 West Indies seem to be migrants from the United States and Mexico with 

 the exception of C. partita which probably entered from Brazil; no species 

 found in the islands so far is peculiar to them, but all are members of more 

 or less predominant continental species. 



Owing to the nature of their structure, fossil remains, so far as recorded, 

 are lacking and an estimate as to the age of the plants in relation to the 

 earth's history would be valueless. 



