io8 



BACTERIA IN RELATION TO PLANT DISEASES. 



METHODS OK INOCULATION. 



Inoculations niav Ije b}' punctures with a delicate needle (fig. 91), by abrasions of 

 the surface, b\' Inpoderniic 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 e\-aporation for some hours, or on a larger scale by spraying portions 

 of the surface with ver\- dilute culture fluids or, preferably, with water coirtaining 

 the Ijacteria (figs. 92, 93, 94), by brirshing 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 natiu'e on dewy nights 

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

 sand, atomizing thoroughly with sterile water and covering with tall, room^■ bell-jars. 

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



the right conditions have been obtained, moisture 

 co\-ers the surface of the plant in tin)- drops which 

 do not evaporate. The bell-jar mav 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 spraving, it should be covered 

 with cloth or paper to protect from the light. 

 Usuall)' 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 ver)- 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 ser\'iceable for obtaining conditions similar to those prevailing in wet 

 weather. The}' ma)- be left on i to 3 days, the outside of the tent as well as the 

 plants within being spra)ed with water often enough to keep evervthing moist 

 until infections ha\'e Ijeen secured. 



When the nature of the plant will permit it and ^\-hen onh' a few inocula- 

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

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



F,g. 93.^ 



"'Fic. 93. — Atomizers for u^r witli the air-tank ( fig. 92 ). Tliesc arc made by tiie Davidson Rubber 

 Company, ]"'.o-,toii, Mass. ;\liont one-fourtli aetual si/e. Tlie I )e Vilbiss spra\'er, made in Toledo, 

 Ohio, and now used liy llie writer, lias several distinet ;idvanta,L;es. It is all metal and can be steril- 

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

 llasks and to the tube leadin,!;; from the compresseiLair tank, and the spray may be directed up, down, 

 or straight ahe;id without changing nozzles. It rcipurcs, however, more force to operate than the 

 D;aidson sprayeis, ami consc'iiuently is less convenient when used witli a hand-bulb. 



