142 BACTERIA IN RELATION TO PLANT DISEASES. 



In table 17 are given the notes of August 5, 7, and 14, 1908, on the growth of two strains 

 of Bacterium stewarti in various media, inoculated August 3 from 4-day-old bouillon cultures 

 proven to be alive by inoculation therefrom to common bouillon which had clouded. The 

 two strains used were (i) McCulloch, isolated from Fairfax, Virginia, corn in 1907; (2) 

 Galloway, isolated from Golden Bantam corn from Dr. B. T. Galloway's Maryland farm, 

 1908. One tube of each medium was used, except acid tomato juice, of which two were 

 used, each tube receiving all the fluid that could be taken up on a 3 mm. loop a drop. 

 Temperature 30 C. Table 18 gives notes on a third strain, and table 19 summarizes 

 the results of reinoculations with each one of the three strains. 



Bad. stewarti produces only a moderate amount of alkali, and in some media, e. g., milk, 

 this is wholly obscured by the moderate production of acid. The following media are usu- 

 ally rendered alkaline to litmus : Beef -bouillon, plain peptone agar, potato cylinders, maltose 

 agar. 



Potato cylinders are usually grayed by Bact. stewarti, but strips of lead acetate paper 

 were not browned by exposure over them for 9 days. Cultures on rutabaga and on yellow 

 globe turnip did not brown the paper nor stain the substratum (64 days) ; white radish was 

 not browned in 64 days. 



Indol. In one set of experiments a slight indol reaction was obtained ; in two others made sub- 

 sequently there was no pink color on adding sodium nitrite and sulphuric acid, but a slight pink color 

 appeared on heating the tubes at 80 C. for a few minutes. The latter were cultures 14 days old in 

 peptone-water, and in peptonized Uschinsky. The question of indol formation must therefore be left 

 an open one. 



Pigments. The yellow pigment is probably similar to that in other yellow species of bacteria, 

 i. e., lipochrome (see vol. II, Bact. hyacinthi). No special studies have been made. Its color varies 

 from buff-yellow to chrome, but is much paler when the supply of free oxygen is scanty. 



The brown pigment formed by this organism does not appear as readily in culture-media as that 

 of Bact. campestre. For instance, cultures of the latter stain cruciferous substrata dark brown in the 

 course of 6 or 8 weeks, while in the same media (radish, rutabaga, yellow globe turnip) Bact. stewarti 

 produces no stain. 



The organism causes a brown stain in the host-plant, but this is perhaps a host reaction. This 

 develops slowly and is usually most conspicuous in the parts longest occupied, i. e.,in the lower nodes. 



Crystals. Crystals occur in old agar cultures. They are prismatic (fig. 63) or jagged X-shaped. 

 They were once seen in cultures on coconut. Contamination (?). 



Enzymes. Our knowledge of the enzymes produced by Bact. stewarti is very imperfect. Cavi- 

 ties are formed in the host-plants, and there must therefore be some substance capable of dissolving the 

 middle lamella although not necessarily an enzyme. The question of the existence of a cytase is an 

 open one. In test-tube cultures, the tissues of potato, coconut, rutabaga, yellow globe turnip, radish, 

 and carrot were not softened. Cane-sugar is inverted, but invertase was not formed in the absence 

 of sugar (beef -broth without peptone). Bacterium stewarti has only a slight action on potato-starch 

 and therefore very little diastase is produced. In this particular it resembles Bact. hyacinthi and 

 differs widely from Bact. campestre. No trypsin and no lab-ferment are produced. Old cultures 

 cause a copious evolution of oxygen from hydrogen peroxide. 



One gram of grape-sugar in 10 c.c. of +15 nutrient agar did not retard the growth of Bact. 

 stewarti in streak-cultures; on the contrary, growth was stimulated from the start, being in 48 hours 

 four times as great, and at the end of a week at least five times as great as in the check-tubes. 



Vitality. Bacterium stewarti lives for a considerable time on culture-media, especially on agar, 

 in milk, and in Uschinsky's solution. It was dead on agar in the ice-box at the end of 17.5 months. 

 It was alive under similar conditions on the same medium at the end of 14 months. It lived in litmus 

 milk for 7 months and in Uschinsky's solution for 4 months. It remained alive in a variety of culture- 

 media for more than 2 months. 



Mixed cultures and infections. In the host-plant the organism often occurs in pure cultures. 

 Nothing is known respecting mixed infections, or the effect of other organisms on this one in mixed 

 cultures. In pure culture the organism does not readily lose its power to infect maize. 



Germicides. Very little is known respecting the behavior of this organism toward antiseptics 

 and germicides. 



