METHODS OF RESEAECH : STUDY OF CULTURES 111 



various lightings, enlarged ten times (that being recommended 

 as a convenient standard magnification). This is so useful for 

 purposes of comparison (Figs. 25, 114, 230, 254) that I have 

 made it a routine practice in my laboratory for several years. 

 In particular, oblique transmitted light will often reveal an inner 

 colony-structure (Figs. 13, 37, 69, 275) not visible on the surface 

 or by direct transmitted light. 



METHODS OF INOCULATION 



Needle Punctures. — I have made much greater use of the 

 needle than of any other instrument in making inoculations. 

 Its wounds are slight. It carries into the plant a minimum 

 quantity of the organism to be tested and inoculations made in 

 this way conform more nearly to natural methods of infection 

 than do those produced by instruments making coarse wounds 

 and introducing excessive numbers of bacteria. I am always 

 suspicious of results that can be obtained only by drenching 

 and swamping tissues with foreign organisms. 



Syringes. — Those injection syringes are to be preferred which 

 are simple in construction, easily separable into a few parts for 

 cleaning, and not liable to spirt out fluids around the piston. 

 The piston and barrel should be of glass, the latter, of course, 

 graduated, at least to tenths of cubic centimeters. They are 

 seldom necessary in plant pathological work. 



Infection Cages. — Cages 2 feet deep by 2 feet high by 3 feet 

 wide are most convenient. They should have a strong sash 

 frame open at the bottom but set on all sides (including the top) 

 with window glass, and the whole front should consist of two 

 swing doors closing against each other in the center and closing 

 at the bottom on a 2-inch baseboard. Such cages will hold eight 

 8-inch pots. Each time before use they should be autoclaved. 

 In absence of conveniences for this they should be wiped inside 

 with mercuric chlorid water a day in advance of use. Plants 

 on which bacterial suspensions have been sprayed may be ex- 

 posed to moist air in such cages 48 hours without harm. 



Soil Inoculations. — The earth may be sprayed or drenched 

 with water suspensions of the bacterial cultures, or infected 

 by burying in it recently diseased plants. At the same time 



