WILT OP CUCURBITS. 



295 



potato is same color as the ungrayed substratum; usually it grays potato after a time; 

 clouds peptone-bouillon and Dunham's solution thinly; growth retarded in acid juice of 

 cucumber-fruits; also retarded or inhibited by juice of many other vegetables, e. g., table 

 beet, sugar-beet, turnip, etc.; grows on many media at 25 C., carrot, coconut, Fermi, 

 Uschinsky, etc.; asparagin as carbon food (?); thermal death-point 43 C.; optimum for 

 growth 25 to 30 C. ; maximum, 34 to 35 C. (?) ; minimum (?) 8 or below; easily killed by 

 dry air, sunlight, or freezing (50 per cent or more); ammonia-production (moderate); 

 feeble production of hydrogen sulphide; in litmus- 

 milk persistent growth without reduction or distinct 

 change in color of litmus; short lived on many 

 media; killed readily by acids, but lives long in cane- 

 sugar-bouillon with carbonate of lime; grows on 

 some media in hydrogen and carbon dioxide; dis- 

 solves middle lamella (cucumber-parenchyma); dis- 

 tributed by insects especially by Diabrotica vittata. 

 Group No. 222.2322023. 



NEGATIVE. 



Mealy or dendritic surface growths; Gram's 

 stain; endospores; chains; filaments; growth not yel- 

 lowish, piled up or wrinkled ; pellicle on bouillon ; lique- 

 faction (gelatin,* blood-serum, egg-albumen, etc.); 

 lactose and pure maltose in closed end of fermenta- 

 tion-tube; lab ferment; acid (in milk) ; gas (all media) ; 

 pigment (except gray stain on potato) ; indol ( ?) ; 

 nitrite from nitrates; starch-splitting; cellulose-dis- 

 solving (except possibly in host) ; asparagin as nitro- 

 gen food ; ammonium salts as nitrogen food ; steamed 

 turnip, and cauliflower; Cohn's solution; acid bouillon 

 (+33); acid gelatin; nearly odorless; not a soft rot; 

 not infectious to tomato, potato, etc. On steamed 

 potato liable to be confounded with a non-infectious 

 coccus (follower) which reddens litmus milk. 



Any organism which reddens or blues litmus-milk decidedly, reduces the litmus, throws 

 down the casein, or clears litmus-free milk without precipitation may be set down at once 

 as something else. 



TREATMENT. 



So far as known this disease is disseminated only by means of insects, consequently 

 the first effort of the grower should be to reduce the number of these pests to the lowest 

 possible terms. Various suggestions for the destruction of these insects have been made 

 by entomologists, the most hopeful of which is perhaps, to trap the leaf-eating beetles by 

 sowing between the rows or in the vicinity of the cultivated plants, other plants which 

 these beetles are very fond of feeding upon. Subsequently both plants and beetles should 



*According to Barlow this organism grows better on potash gelatin than en ordinary gelatin, and slowly liquefies 

 that medium both in plates and stab-cultures. 



fFio. 94. Culture of B. tracheiphihis showing limited growth in the absence of air. A tube of nutrient agar was 

 boiled one hour, slanted, cooled, and immediately streaked, forming a. Upon this b was then poured after boiling one 

 hour and cooling to a safe temperature. As soon as b had solidified a third tube of agar was melted, cooled, and poured 

 into the tube, forming c. In 4 days there was a distinct whitish growth the whole length of the slant. Subsequently 

 colonies developed all through b and c but were visible to naked eye only at junction of b and c and in the upper 4 to 5 

 mm. of c, i.e., in that part freest to absorb air. The agar contained beef-broth, Witte's peptone, and a moderate 

 amount of sodium carbonate. 



JFiG. 95. Stab-culture of B. tracheiphilus on acetic acid agar. Growth long delayed, discrete, and finally appearing 

 mostly on one side where agar had shrunk from wall, i. e., not in stab. This sketch shows appearance after 33 days. 



Fig. 94.f 



Fig. 954 



