CONTROL OF ANIMAL PARASITES 265 



everywhere, often destroying entire crops and making it 

 necessary to sterilize the soil with live steam or to remove 

 all the earth frequently and disinfect the benches. In the 

 South they are often most serious pests of outdoor garden 



FIG. 117. Portion of cyst wall (T. 

 After Braun 



and field crops. This whole side of plant injury, however, 

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

 of their experiment stations. 1 



General characters. Familiar nematodes are vinegar eels, 

 hair snakes, and the large, round worms so common in dogs, 

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

 from microscopic size to 1 or 2 feet in length. Many are 

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

 but great numbers are parasitic. The life cycle of parasitic 



1 Nematodes bore into the roots and cause worm-swellings, galls, and knots. 

 The plants most seriously attacked (Scholield) are beets, carrots, celery. 

 cucumber, eggplant, lettuce, muskmelon, watermelon, clover, cowpeas, 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 tomato plants. See 

 Bessey, " Root-Knot and its Control," Bulletin No. 217, Bureau of Plant 

 Industry, United States Department of Agriculture, 1911 ; Schofield, Bureau 

 of Plant Industry, United States Department of Agriculture, Circular 91 ; 

 and Cobb. Yearbook, United States Department of Agriculture, 1014, 

 pp. 457-490 (19 illustrations). 



