PLANTS AS DISEASE PRODUCERS 299 



barren region of New Jersey. The family Scrophulariace^ includes 

 a number of these root parasites. Such are the eyebright {Euphra- 

 sia), yellow-rattle {Rhinanthus), cow- wheat (Melampyrum), lousewort 

 (Pedicularis) and others. The suckers of the yellow-rattle are of 

 considerable size : their margins are swollen and they spread around the 

 roots of the hosts. Those of the cow-wheat resemble in general those 

 of the yellow-rattle. In America species of Agalinis (old genus Gerardia 

 in part) are known to have parasitic attachments to the roots of various 

 plants. This plant is a member of the family Rhinanthacece (Scroph- 

 ULARiACE^, tribe Rhinanthae). 



The second series comprises the chlorophylless root parasites, such 

 as Lathrcea squamaria, the toothwort. The young seedling lives at 

 first upon the reserve substances of its seed, sending out roots in all 

 directions. These finally fasten to the roots of ash, hornbeam or 

 poplar, by means of a sticky sucker, which develops a central core 

 that penetrates into the roots of its host. Colorless shoots covered 

 with whitish scale leaves are formed and the flowering shoot which 

 develops above ground has a purphsh hue. 



The third series of parasitic flowering plants includes those of the 

 families Orobanchace^, Balanophorace^ and Hydnorace^. One 

 genus, Orobanche, the broom-rape genus, is sufficiently common to merit 

 attention (Fig. 117). The embryo of Orobanche shows no trace of root 

 and stem and is without cotyledons. It is a spiral filament of delicate 

 cells feeding on the stored reserve food. In its downward growth, its tip 

 traces a spiral line until it finds the roots of a congenial host, when it 

 not only adheres firmly to a root, but swells in such a way as to assume 

 a flask-shaped appearance. The thickened part becomes nodulated 

 and papillose and some of the papillae form conic pegs, which penetrate 

 into the root of the host until the vessels of the parasitic attachment 

 of the broom rape reach the vessels of the host. A bud is formed at 

 the point of union between host and parasite and a strong thick flower- 

 bearing stem grows above ground. Closely and intimately associated 

 with a host, such as a clover plant, the broom-rape does considerable 

 damage. Conopholis americana ,(Fig. 118) and C. mexicana live as 

 parasites on oak roots, developing large swelhngs out of which the 

 flowering shoots grow. 



The writer collected Conopholis mexicana in 1896 on the roots of 

 an oak, Quercus reticulata, on the mountains at Eslava (10,000 feet) 



