180 Principles of Plant Culture. 



minate in the soil, and the young plants attach them- 

 selves to the roots of their host which they enfeeble by 

 robbing them of nourishment. In the ease of hemp, 

 the parasite also injures the quality of the fibre. 



Preventives. The seed of hemp or tobacco should not 

 be taken from ■ a crop infested with broom rape. In- 

 fested fields should be planted for several years to 

 some crop not attacked by broom rape, as potatoes, In- 

 dian corn, beans, grains or grasses. In infested crops, 

 the broom rape should not be permitted to mature its 

 seeds. 



320. The Dodders of Clover and Flax* are the most 

 injurious of their class. The young plant attaches it- 

 self to the stem of its host, about which it twines, rob- 

 bing it of nourishment by means of small suckers. 



Preventives. The seeds of dodder are somewhat 

 smaller than those of clover or flax, and hence may 

 be separated from the latter by sifting. Badly infested 

 ground should be devoted for two to four years to a 

 crop not attacked by the dodder. 



b — Plants as affected by Fungous Parasites. 



321. The Fungi constitute an extensive class of 

 plants that derive their nourishment wholly from or- 

 ganic matter. Many of them are injurious to culti- 

 vated plants. Unlike the harmful insects, most of which 

 work their ravages within full view, the fungi are in 

 many cases discernible only with the microscope, 

 and reveal their presence only by the death or injury 

 of their host. The fungous parasites are very numer- 



• Cuscuta trifolia, C. Epilinum. 



