44 Trans. Acad. Sci. of St. Louis. 



In regard to the factors bearing upon the possibility 

 of transportation it might be mentioned that these forms 

 are practically helpless in regard to their locomotion, 

 yet in regard to duration of life when off a host, I found 

 that forms would live easily for four days in minute 

 scrapings. Doubtless under favorable circumstances 

 they would live much longer. What then are the condi- 

 tions which cause such a contradictory distribution of 

 the species? Some forms have been able to adapt them- 

 selves to hosts not closely related; others can not live 

 except upon a single host. I can not give any very sat- 

 isfactory answer to this question, but merely suggest that 

 it is because some species have either a much more deli- 

 cate taste or more delicate digestive systems than other 

 forms, and for this reason have remained upon a single 

 host species. 



A List of the Eriophyidae Known to Occur upon More 

 THAN One Host Species, Together with Their 

 Hosts. 



Eriophyinae. 



eriophyes Sieb. 



E. tenuis (Nal.) — Avena pratensis L., Bromus arvensls L., B. erectut 

 Huds., B. mollis L., Dactylis glomerata L. 



E. laevis (Nal.) — Alnus glutinosa Gart., A. incana D. C, A. virldls D. C. 



E. trevitarsus (Focken) — Alnus glutinosa Gart., A. incana D. C, A. 



viridis D. C. 



E. rudis (typlcus) (Can.) — Betula verrucosa Ehrh., B. pubescens Ehrh. 



E. rudis longisetosus (Nal.) — Betula verrucosa Ehrh., B. pubescens 



Ehrh. 



E. lionotus (Nal.) — Betula verrucosa Ehrh., B. pubescens Ehrh. 



B. ilicis (Can.) — Quercus Ilex L., Q. ithaburensis Decne. 



E. populi (Nal.) — Populus tremula L., P. nigra L. 



E. tetanothrix (Nal.) — Salix fragilis L., S. aurita L. 



E. drabae (Nal.) — Alyssum calyclnum L., A. hirsutum M. B., Berteroa 

 incana D. C, Camelina satlva Crantz, Capsella 

 bursa-pastorls L., Erysimum canescens Rth., Lepld- 

 ium draba L., Sisymbrium sophIa L. 



E. rosalia (Nal.) — Helianthemum fumana Mill., H. hirsutum Th., H. 

 oelandicum Wahlb. 



