44 



THE FUNGI WHICH CAUSE PLANT DISEASE 



B. haria Hori & Miy. is a parasite of the Japanese basket 

 willow."' 



B. hyacinthi septicus Heinz,'-" is recorded as the cause of a soft 

 white rot of the hyacinth. 



B. lactucae Vogl. is said to cause a lettuce disease."' 

 B. lycopersici Hegyi has been described as the cause of a rot 

 of tomatoes. ''- 



B. maculicola Del. is regarded as the cause of a tobacco leaf 

 spot.'" 

 B. melanogenus P. & M.'"is recorded in England on potatoes. 

 B. melonis Giddings."^ 



An actively motile bacillus, 0.6-0.9 x 1-1.7 n; flagella 4-6 

 peritrichiate; no spores. Gram negative. Bioth strongly clouded, 



no pellicle or ring, 

 slight sediment. Agar 

 stroke slimy, glistening 

 translucent; colonies 

 round or amoeboid. In 

 gelatine stab hquefac- 

 tion infundibuliform in 

 two days. Milk co- 

 agulated with abun- 

 dant gas. Nitrite pro- 

 duction abundant ; indol 

 slight. T. D. P. 49- 

 50°. Opt. 30°. The 

 vegetables rotted were 

 muskmelon, citron, car- 

 rot, potato, beet, cu- 

 cumber and turnip. 



In the soft rot caused 

 by this organism in 

 muskmelons, motile 

 bacteria were observed in abundance by Giddings in 1907. Plating 

 gave pure cultures which by inoculation tests were shown to be 

 those of the causal organism of the rot. Decay is produced by 

 solution of the middle lamella by enzymic action, the remainder 

 of the walls withstanding the attack. The bacteria are thus 



Fig. 29 .-y Photomicrograph of B. melonis. .1, show- 

 ing living organisms in agar hanging block cul- 

 ture; b, with flagella stained by Lowitz method. 

 After Giddings. 



