132 BACTERIA IN RELATION TO PLANT DISEASES. 



The slime finds its way to the inner surface of the husk more readily than to the outer 

 surface, but sometimes it reaches the latter also. It generally comes to the surface through 

 stomata (figs. 49, 50, 51, 52). The only conspicuous parts in which the slime has not been 

 seen are the floral organs and the silicified outer parts of the stem. Even the latter state- 

 ment must be modified somewhat as a result of the observations recorded in 1908, since 

 rarely the bacteria may be seen issuing from small cracks in the siliceous covering of the 

 internodes, especially where protected by the leaf-sheaths. Probably the stigmas (silks) 

 are never infected, they are so fugitive, but the male flowers might well be infected, since 

 the writer has traced the infection well up into the main axis of the male inflorescence a 

 number of times. 



As yet we do not know how the wall of the vessel is pierced. It is probable that cellu- 

 lose is not destroyed. 



THE PARASITE. 



Bacterium stewarti EFS.* as it occurs in the vessels of the maize plant and in young 

 cultures on ordinary culture media is a short rod under i/i in diameter and generally less 

 than 4/i in length, with rounded ends (fig. 59). It occurs singly, in pairs, or fours, joined 

 end to end. According to Stewart the organism usually occurs in pairs with a plain con- 

 striction. "A pair varies in length from 2.5/x to 3.3/4 and in width or diameter from 0.65,11 

 to 0.85/1." My own measurements do not differ materially. The following are average 

 measurements taken from organisms grown in various media: 



Measurements made July 21,1 909, from potato-cultures 4 days old gave the following results : 



Amyl Gram stain gave 1.3 to 2.imX 0.4 to 0.611; carbol-fuchsin gave 0.9 to 2.0^X0.3 to 0.7^. On some of the slides 

 the carbol-fuchsin seemed to have contracted the protoplasm into small lumps. 



Agar streak-cultures 2 days old gave the following results : 

 Amyl Gram, 0.9 to 2.0/j X 0.4 to o.7m; carbol-fuchsin, 0.9 to 1.7^1 X 0.4 to 0.6/i, 



Taken direct from the vessels of the maize plant, the following measurements were obtained: 



Bacterium stewarti, stained in the tissues (material from Jamaica, Long Island), measured 1.1 to 1.5^X0.5^1. 

 A smear preparation from the Long Island sweet-corn stained by carbol-fuchsin measured 0.9 to 1.4/1X 0.4 to 0.55^. 

 Stained in section from a corn husk taken from the Flats experiment, slide 477 c i.the organism measured 1 to 1.4MX 

 0.4 to 0.5M- 



The general appearance of the organism is shown in figs. 59 and 60. The organism 

 on media is slightly viscid at times and undoubtedly possesses a capsule, although no efforts 

 have been made to demonstrate it by means of special stains. The only very viscid masses 

 seen are those mentioned under examination of diseased plants in 1908. 



The organism is motile, especially in young cultures, and the writer has demonstrated 

 a polar flagellum (fig. 60). Usually, at least, only one flagellum is present on the end of 

 each rod. Long chains or filaments have not been observed. So far as known the organism 

 does not produce endospores. Small clumps and bunches of the bacteria (pseudozoogloeae) 

 occur in various media as follows: Uschinsky's solution, nitrate bouillon. 



The organism stains readily with various anilin dyes. The writer has tried the follow- 

 ing with fairly good results: Carbol-fuchsin, Loeffler's alkaline methylene blue, amyl Gram. 



Gram's stain gave negative results or at least not a deep stain. The rods were visible 

 with wide-open diaphragm, but were only a pale blue. 



When cultivated in salted peptone water containing methylene blue the bacterial pre- 

 cipitate was stained a deep blue, the pigment in the fluid remaining unreduced and bright 

 blue or greenish-blue in color. Repeated in 1908 with same result, i. e., bacteria distinctly 

 blue both to the naked eye and under the microscope. 



*Syn. Pseudomonas stewarti EFS. 



