77° 



ECOLOGY 



sia Arnoldii. Among the commoner partial parasites are various 

 mistletoes (as Viscum and Phoradendron, fig. 1084) and a large number 

 of the Scrophulariaceae, especially in the tribe Euphrasieae (as Melam- 

 pyrum, Rhinanlhus, and Euphrasia); all such plants differ from the 

 holoparasites in containing chlorophyll. 



Holoparasitic seed plants differ from their autophytic relatives not 

 only in the presence of haustoria and in the absence of chlorophyll, but 



Fig. 1083. — Individuals of a holoparasite, Orobanche fasciculala, attached to the roots 

 of an Artemisia; note the stages between young seedlings which appear like root swellings 

 and adult plants with opening flowers ; note also that the parasite is attached to the host 

 at but a single point; Gary, Ind. — Photograph by Fuller. 



also in the relative absence of leaves, whose place is taken by insig- 

 nificant and probably functionless scales. As among fungi, the higher 

 holoparasites may be plurivores (e.g. Cuscuta Gronovit) or univores ; 

 examples of the latter are the flax dodder (Cuscuta Epilinum) and 

 Orobanche Hederae, a parasite on the English ivy. The European 

 mistletoe, Viscum album, usually is regarded as a plurivore, but the 

 presence of physiological species is suggested by the fact that the fir 

 mistletoe does not grow on the pine, nor vice versa; the form that in 



