30 THE FUNGI WHICH CAUSE PLANT DISEASE 



it again caused disease. More than a hundred inoculations by 

 scarification or puncture gave one hundred per cent infection. 

 Controls remained undiseased. Infection, stomatal or water pore, 

 was also secured through the apparently unbroken epidermis. 



The virulence of the or- 

 ganism was retained after 

 five months on agar. It 

 is believed that the usual 

 mode of infection is 

 through rifts in the epider- 

 mis due to frost and that 

 the germ is wind-borne 

 from infected soil. 



Ps. michiganense (E. 

 F. Sm.) Stev. (Group 



number -22. 252-.) 



Rod short with roimded 

 ends, 0.35-0.4 x 0.8-1.0 fi. 



Fig, 16.— Ps. medicaginis; 48-hour agar-culture, No motility Seen from 

 showing formation of aaments. After Sackett. gtems. Flagella apparently 



polar but not seen distinctly. Agar colonies pale-yellow, smooth, 

 round. Agar stab canary-yellow, opaque, viscid. Bouillon moder- 

 ately clouded, a moderate slimy precipitate; no rim or pellicle. 

 Gelatine not liquefied. , 



The organism was described by Smith ^^ as the cause of a stem 

 disease of tomatoes in Michigan. No fungi were seen but bacteria 

 were present in great numbers in the bundles also in cavities in 

 the pith and bark. The organism was isolated and the disease was 

 produced both by pure culture inoculations and by crude inocula- 

 tions, using an impure inoculum. The disease caused is less rapid 

 in development than that caused by B. solanacearum and less 

 browning of the infected tissue occurs. 



Ps. mori (B. & L.) Stev. (Group number 222. 202-.) Rod 



with rounded ends, 1.8-4.5 x 0.9-1.3 fi, mostly 3.6 x 1.-2 m; 

 motile by one, sometimes two polar flagella. No spores. Pseudo- 

 zoogloeffi present. Agar colonies round, smooth, flat. Agar 

 streaks spreading, flat, dull-white. Gelatine stab filiform, no 

 liquefaction. Milk not coagulated. No gas. T. D. P. 51.5°. 



