XVI LIST OF ILLUSTRATIONS 



Fig. Page 



31. Peg or rake steam sterilizer used by some growers at 



Toledo, Ohio 95 



32. Peg steam sterilizer in operation at Toledo, Ohio 97 



33. Apparatus for formalin sterilization. (W. T. Water 



Tank. F. T. Formalin Tank. G. Waterglass gauge 

 to show quantity of formalin. A. Air cock. V. 

 Valve. F. Funnel. E. Air pipe to maintain same 

 pressure in both tanks. D. Drain-off cock. H. and 

 R Supports. B. Base. O Outlet. S. Glass tube 

 through which the formalin drops to tank below 98 



34. Garbage can suspended to wire, used in fumigating with 



tobacco stems 107 



35. Female nematode (Heterodera radicicola) magnified 85 



diameters; a, mouth; b, spherical sucking bulb; c, 

 ovaries as seen through the body wall; d, anus; e, 

 small white spots showing approximately the natural 

 size of these worms. They are usually white. It is 

 generally not difficult to isolate them in water by 

 breaking open the galls containing them. (After 

 N. A. Cobb) 113 



36. Male nematode: I, Worm in profile view; II, head of 



the same, more highly magnified; III, middle region 

 of the worm, showing blind ends of the sexual 

 organs; IV, posterior extremity. The drawings were 

 prepared from stained specimens, examined in car- 

 bolic acid solution, a, lips ; b,. cesophageal tube ; c, 

 median bulb; d, excretory pore; e, spear; f, intes- 

 tine ; g, blind ends of testicles ; h, testicles ; i, 

 spicula; j, rudimentary bursa; k, anus. (After 

 N. A. Cobb) 114 



37. Galls on cucumber roots produced by nematodes 115 



38. Roots of tomato plant completely invaded by gallworms. 



(After George F. Atkinson) 116 



39. Galls on lettuce roots caused by nematodes 118 



40. White fly (Aleyrodes vaporariorum) : a, egg; b, young 



larva; c, pupa, top view; d, pupa, side view; e, 

 adult c, d, e, about 25 times natural size ; a, b, still 

 more enlarged (a-d, after Morrill, Tech. Bui. Mass. 

 Exp. Sta. ; e, original) 111) 



41. Two nurseries in a four-acre Boston range. Note let- 



tuce seedlings of different sizes 134 



42. Nursery in large range near Boston. Head lettuce 



plants 135 



43. Flat of Grand Rapids lettuce seedlings 136 



44. Flat of lettuce plants ready for transplanting into the 



beds 137 



