loS 



BACTERIA IN RELATION TO PLANT DISEASES. 



METHODS OF INOCULATION. 



Inoculations may be by punctures with a delicate needle (fig. 91), by abrasions of 

 the surface, by hypodermic injection, by watering the soil with infective material, by 

 plunging aerial parts into infectious liquids for a longer or shorter time, by simply 

 putting the bacteria into drops of water on parts of the plant and protecting from 

 sunlight and evaporation for some hours, or 011 a larger scale by spraying portions 

 of the surface with very dilute culture fluids or, preferably, with water containing 

 the bacteria (figs. 92, 93, 94), by brushing or rubbing cultures into some part of the 

 surface, by allowing insects, snails, etc., to feed on diseased material and then colo- 

 nizing them on healthy plants. The writer has made good use of this last method in 

 case of three different bacterial diseases. Stomatal infections may be secured by sub- 

 jecting the plants to conditions similar to those occurring in nature on dewy nights 

 or during heavy fogs or prolonged rains, i. e., by placing the potted plants on wet 

 sand, atomizing thoroughly with sterile water and covering with tall, roomy bell-jars. 

 The experiment should be undertaken in a cool rather than a warm house. When 



the right conditions have been obtained, moisture 

 covers the surface of the plant in tiny drops which 

 do not evaporate. The bell-jar may now be raised 

 and the plant again atomized lightly with steril- 

 ized water containing the bacterium. The best 

 time to do this is late in the afternoon, so as to 

 take advantage of the cooler night temperature. 

 When the bell-jar is returned, which should be 

 immediately after spraying, it should be covered 

 with cloth or paper to protect from the light. 

 Usually bell-jars should be removed at the end 

 of twenty-four hours, but exceptionally they may 

 be left on thirty-six to forty-eight hours, if not 



exposed to the sun. Inoculation cages are very convenient for small plants (fig. 95). 

 In case of trees, or shrubs, or masses of tall herbs, tight-fitting covers of tent-cloth 

 will be found serviceable for obtaining conditions similar to those prevailing in wet 

 weather. They may be left on i to 3 days, the outside of the tent as well as the 

 plants within being sprayed with water often enough to keep everything moist 

 until infections have been secured. 



When the nature of the plant will permit it and when only a few inocula- 

 tions are to be made, the surface which is to be punctured should be rubbed thor- 

 oughly for three to five minutes with mercuric-chloride water (1:1000) and then 



*Fic. 93. Atomizers for use with the air- tank (fig. 92). These are made by the Davidson Rubber 

 Company, Boston, Mass. About one-fourth actual size. The De Vilbiss sprayer, made in Toledo, 

 Ohio, and now used by the writer, has several distinct advantages. It is all metal and can be steril- 

 ized in boiling water without becoming twisted out of shape, it can be attached more easily to large 

 flasks and to the tube leading from the compressed-air tank, and the spray may be directed up, down, 

 or straight ahead without changing nozzles. It requires, however, more force to operate than the 

 Davidson sprayers, and consequently is less convenient when used with a hand-bulb. 



