EELWORMS. 



79 



is not a plant parasite. 

 The most important genera 

 living in plant-tissues are 

 Tylenchiis, Aphelenchus, 

 and Heterodera. The 

 former genus also lives in 

 the earth and in rootage 

 of plants. The genera 

 Dorylaivius and Aphelen- 

 diiis also live under similar 

 conditions. Tylenchus and 

 Heterodera produce, the 

 worst diseases. 



These undergo part of 

 their life - cycle in the 

 earth and part in their 

 plant host. 



The three most typical 

 forms are — (1) the Wheat 

 Eelworm [Tylenchus scan- 

 dens) ; (2) the Stem Eel- 

 worm {T. devastatrix) ; and 

 (3) the Beet Eelworm 

 {Heterodera scliachtii). 



The Wheat Eehoorm (T. 



seandens = T. tritici of 



Bastian). 



Length about one- 

 twelfth of an inch in 

 the male and one - tenth 

 to one-fifth in the female. 

 These minute white or 

 almost transparent worms 

 are the cause of a disease, 



Fig. 29. — Eelworms {AnguilluU 

 i. Tylenchus devastatrix, from clover roots; ii. 

 ovum ; iii. anterior extremity ; iv. posterior ex- 

 tremity of male. (After Kitsema Bos.) Greatly 

 enlarged. 



