COXTKUL OF ANLMAL PARASITES 



265 



everywhere, often destroying entire crops and making it 

 necessary to sterilize the soil with live steam or to renK)vc 

 all the earth frequently and disinfect tlie benches. In tiie 

 South thev are often most sericjus pests of outdoor garden 



Fig. 117. Portion of cyst wall {T. ecbinocorxu^) 



After Bniuu 



and iield crops. This whole side of plant injuiy, however. 

 we must leave for interested pupils to work up. with the aid 

 of their experiment stations.^ 



General characters. Familiar nematodes are vinegar eels, 

 hair snakes, and the large, round worms s(^ common in dogs, 

 horses, and man. As seen from these examples, they vary 

 from microscopic size to 1 or "2 feet in length. Many an* 

 free-living in water (marhie and fresh) or in damp ground, 

 but great numbers are parasitic. The life cycle of parasitic 



' Ncmatode.s bore Into the roots and cause worni-swellinjis, galls, anil knots. 

 The plants most seriously attacked (Scholield) are l)eets, carrots, celery, 

 cucumber, eggplant, lettuce, musknielon, waternielcm, clover. co\vpea.s rape, 

 soy beans, catalpa, cherry, elm, and peach. They are most often distributed 

 in nursery stock and seed potatoes, which should be most carefully examined 

 for them before planting, especially strawberry and ti^mato plant.s. — See 

 Bessey, "Root-Knot and its Control," liuUdin No. :in. Bureau of riant 

 Industry, United States Department of Agriculture. T.Ul ; Schotield, Bureau 

 of Plant Industry. United States Department of Agriculture, Cirndav 91 ; 

 and Cobb. Yearbook, United Statrs D.-partment r.f ALn-iculture. l'.»14. 

 pp. 457-490 (I'J illustrations). 



