174 PRINCIPLES OF PLANT CULTURE 



crop not attacked by broom rape, as potatoes, Indian 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 (Cuscuta epithy- 

 mum, C. epilinuni) are the most injurious of their class. 

 The young plant attaches itself to the stem of its host, 

 about which it twines, robbing 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. 



321. Parasites of the lower orders, spore plants. — 

 The lower parasites include the fungi and bacteria.^ 

 These two groups are, however, so similar that we need 

 here only call attention to the fact that the bacteria are 

 even more minute than the fungi and as a rule more 

 difficult to combat. These minute plants, fungi and 

 bacteria, constitute an extensive group of organisms which 

 derive their nourishment from organic matter. Most of 

 them are saprophytes living in dead organic materials, 

 but others are parasites (25) upon the higher plants or 

 animals, causing various diseases. Unlike the harmful 

 insects, most of which work their ravages within full 

 view, the bacteria and fungi are in most cases discernible 

 only with the microscope, and reveal their presence only 

 by the death or injury of their host. These parasites 

 are very numerous and exhibit great diversity of structure 

 and habit. Some of them live only upon enfeebled plants, 

 while others attack healthy ones. Some, as the pea mildew, 



1 Singular, fungus, plural, fungi; singular bacterium, plural, 

 bacteria. 



