. Carnegie Institution of Washington publication. '32 BACTERIA IN RELATION TO PLANT DISEASES. until the third day. Surface colonies brown faster than buried ones, which would seem to indicate that air is necessary for the formation of the pig- ment. The browning of surface colonies is distinct at the end of 15 days.* Stab growth is best in upper part of the agar. On slant agar during the first 10 days there is a thin, white, smooth, wet- shining streak and a small amount of white pre- cipitate in the fluid of the V. There are no crystals and no stains in the agar. The surface colonies on nutri
. Carnegie Institution of Washington publication. '32 BACTERIA IN RELATION TO PLANT DISEASES. until the third day. Surface colonies brown faster than buried ones, which would seem to indicate that air is necessary for the formation of the pig- ment. The browning of surface colonies is distinct at the end of 15 days.* Stab growth is best in upper part of the agar. On slant agar during the first 10 days there is a thin, white, smooth, wet- shining streak and a small amount of white pre- cipitate in the fluid of the V. There are no crystals and no stains in the agar. The surface colonies on nutrient agar incline to be irregularly round. Only a few of the colonies are perfectly circular, but at the same time they are not lobed or fingered. They are wet-shining and smooth; ringed growths are sometimes visible in the colonies. The general ap- pearance of the colonies on agar plates is shown in plate 37. The brown pigment from the tobacco organism grown on agar or potato is soluble in water, ethyl alcohol (absolute), and glycerin, but not in chloro- form, turpentine, xylol, benzine, petroleum ether, rhigolene, or benzole. Gelatin stabs.—No liquefaction; not even after several weeks. Growth slight at 140 C. (For kind of gelatin used see Vol. I of this monograph.) Potato.—Much like Bacterium solanacearutn (pi. 41, fig. 4). Very milky turbid growth in fluid around potato during the first 10 days. Old browned potato cylinders when mashed in an abundance of diluted alcohol-iodine gave a deep purple-blue reaction. In another test the color reaction of the mashed potato cylinders is recorded as "deep ; Standard ( + 75) peptonized bouillon.—After 20 days, no pellicle, little or no rim, slight in one or two tubes but not black, uniformly and well clouded, with about 10 mm. breadth of dirty gray-white precipitate. The cloudy bouillon does not now look turbid (flocculent) to the naked eye. A pencil is barely perceptible behind two of these tubes; it can not be
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