134 



BACTERIA IN RELATION TO PLANT DISEASES. 



surface growth, which was plainly yellow and rough granular (possibly ? from the presence 

 of the crystals). It covered only a part of the surface and was between Ridgway's buff- 

 yellow and deep chrome in color. 



A month later there was a very good growth, the surface was wet-shining and not then 

 granular, but covered with little denser masses of the bacteria, resembling colonies growing 

 on the older growth. 



In stab-cultures in 6 per cent glycerin agar the organism grew nearly or quite the 

 whole length of the stabs, but best toward the top. The surface growth increased slowly, 

 so that finally most of the surface was occupied. The growth was pale yellow, particularly 

 at first. Surface smooth or slightly irregular. Streak-cultures also grew. 



On silicate jelly (see vol. I) Bad, stewarti made a very feeble growth. The streak- 

 cultures were under observation 2.5 months. In 2 days 



u there was a very scanty, rough, yellowish growth along the 



line of the streak which did not increase much. A number 

 of organisms were tested. The only other one that failed 



eventually to 



^^^ make a good 



I ^* growth on this 



"1^. medium was Bad. 



vascularum , al- 

 though quite a 

 good many had 

 difficulty in start- 

 ing off, and had 

 made little or no 

 visible growth at 

 the end of 6 days. 

 Bad. stewarti 

 behaves on potato 

 much like Bad. 

 hyacinthi, i. e., 

 out of the water it 

 makes a moderate 

 amount of yellow 

 growth which 



Fi *- 62 -* Fig - 63 ' t soon passes its 



maximum (see this monograph, vol. II, plate 17, fig. 2). The fluid around the cylinder 

 never becomes thickened by the continued development of the organism, and the surface 

 growth ceases for the most part after a week or two, owing to the exhaustion of the small 

 amount of sugar and other soluble foods and the inability of the organism to take its food 

 readily from starch. No gas bubbles appear. The litmus reaction is alkaline. The iodin- 

 starch reaction is always strong in potato-cylinders on which this organism has grown, even 

 when tested immediately under the bacterial layer, although it must have a slight action on 

 starch, since the reaction is generally a deep purple-blue rather than a pure blue, such as 

 the check-tubes yield. The cell-walls of the potato are not softened. The following are 

 notes on a series of 8 cultures (from as many plants) on potato-cylinders in test-tubes : 



*Fio. 62. a. Streak-culture of Bacterium stewarti on a +15 agar slant 3 days at 27 C., September 1902. 

 6. the same on +15 agar slant 8 days at 26 C., October 1908. 



fFlG. 63. Crystals formed in old nutrient agar-culture of Bacterium stewarti. Photographed down upon the 

 surface (nail-head) of the culture. The dark body in the center is the denser growth along the needle-track. Crystals 

 confined to the surface. X4- The culture had been at a temperature of about 14 C. for many weeks. 



