8b BACTERIAL DISEASES OF PLANTS 



These are the three sorts of microscopes I feel specially 

 disposed to recommend. 



Hand Lens. — A good hand lens, that is, one with a flat field 

 free from chromatic aberration and having a long working 

 distance, is absolutely essential. It should magnify about 6 

 times. Hand lenses having a higher magnification ( X 10 or X 15) 

 are sometimes very convenient, but are of less general use 

 because, owing to their short focus, they will not reach to the 

 center of an agar-stab culture or through the top of a Petri 

 dish. The writer uses a Zeiss X 6 Aplanat which leaves little to 

 be desired. 



4. For Hothouse and Inoculation Experiments 



A large autoclave is necessary very frequently for sterilizing 

 pots, soil, discarded infectious plants, and other things used 

 about the hothouse. It should be large enough to take in a 

 small table, a big inoculation cage, or several 200-lb. sacks 

 of soil at the same time. The steam should be from the engine- 

 house pipes. The apparatus we use is the Merrel and Soule 

 No. 3, made by the Sprague Canning Machinery Company, 

 Hoopeston, Illinois, and sold at $45 (pre-war price). Its 

 depth is 60 inches and its diameter 45 inches. It is serviceable 

 but inconvenient. A larger and more convenient horizontal 

 (canners') autoclave, having a depth of 100 inches and an in- 

 ternal diameter of 44 inches (Fig. 56) is made by the same firm 

 and is called ''R K 1. The Rutter Kettle." It is not a very 

 perfect autoclave but by attaching to it a small pump to remove 

 the air it may be used successfully with steam or may be filled 

 with hydrocyanic acid or other insecticidal gases. The Office of 

 Seed and Plant Introduction of the United States Department 

 of Agriculture has devised several inexpensive convenient pieces 

 of apparatus for destroying the nematodes and fungi in green- 

 house soil by means of steam heat without puddling the earth. 



Fig. 56. — Sterilization room of Office of Seed and Plant Introduction, United 

 States Department of Agriculture, Washington, D. C. The Rutter Steam Kettle 

 in the center. At the extreme left is the pump for removing air from the auto- 

 clave or gas, if used as an insecticidal chamber. {Courtesy of Dr. B. T. Galloway.) 



