380 BACTERIAL DISEASES OF PLANTS 



Determine 



For the organism. Morphology. — Size in microns (when 

 growing rapidly in media the rods are often several microns 

 long — 3 to 6 or more), form, aggregation of elements, i.e., chains, 

 filaments, pseudozoogloeae, etc., motility (on margin of hanging 

 drop), absence of endospores, presence and distribution of flagella 

 (use V. A. Moore's modification of Loffler's flagella stain, or 

 van Ermengem's stain). Try Gram's stain; acid-fast stain; 

 Capsule stains. Do involution forms occur? 



Cultural Characters. — Appearance of colonies on thin-sown 

 agar plates (Figs. 292, 293) and on gelatin plates; in stabs and 

 streaks on agar, ditto on gelatin; behavior in peptone bouillon, 

 in potato broth; try also malated and sugared broths. Growth 

 in nitrate bouillon, Cohn's solution, Uschinsky's solution, milk, 

 litmus milk. Is a lab ferment produced in milk? Behavior in 

 peptone water in fermentation tubes with various sugars, alco- 

 hols, and acids. Try it also in fermentation tubes with potato 

 broth and other plant juices, e.g., apple or pear broth. Is there 

 any clouding in the closed end? Test milk in fermentation 

 tubes. Can you get the results shown in Fig. 295? Determine 

 the nitrogen nutrition of this organism. 



Non-nutritional Environment. — Maximum temperature for 

 growth; minimum? Thermal death-point? Effect of sunHght; 

 of dry air (killed quickly), of freezing (salt and pounded ice), 

 of salted bouillons, of chloroform in bouillon, of acids, of alkali, 

 of germicides. Read Reimer's papers and experiment with vari- 

 ous germicides. 



For the disease. Signs. — Period of incubation (examine 

 morning and night each day); signs in flowers (especially in 

 early stages of the disease — first 72 hours); in shoots (observe 

 that the bark of the shoot may be entirely blackened on the sur- 

 face from the bacterial action and yet for a time the terminal 

 leaves may remain green and turgid. Why?); on leaves: a, di- 

 rect effect, i.e., dark lines running out along the petiole, midrib 

 or side veins, due to bacterial infection from the shoot; b, in- 

 direct effect — black specking, flagging, reddening or browning, 

 due to stem injuries farther down. Note the persistence of the 



