THE FUNGI WHICH CAUSE PLANT DISEASE 



29 



purplish-gray spots 1-3 mm. in diameter, ^o* Pathogenicity on 



this host also on cabbage was proved by inoculation. Its entrance 



is stomatal. 

 Ps. malvacearum, E. F. Sm."'- ''• '""* This yellow organism, 



pathogenic on cotton, much resembles Ps. campestris but its slime 



is more translucent on potato and it 



does not attack the cabbage. It was 



grown in pure culture by Smith and 



successful inoculations were made by 



spraying a suspension of a young agar 



culture of the organism upon cotton 



leaves and bolls. No description has 



been published. 

 Ps. medicaginis Sackett.*^ (Group 



number 212.3332133.) A short rod, 



1.2-2.4 X 0.5-0.8 ii; filaments 20.2- 



37.2 (1 long. No spores; actively 



motile with 1-4 bipolar flagella; cap- 

 sules and zoogloea none. Agar streak 

 filiform, later echinulate, glistening, 

 smooth, translucent, grayish-white; 

 no gelatine liquefaction; bouillon 

 slightly turbid, pellicle on third day, 

 sediment scant. Milk unchanged. 

 Agar colonies round, grayish-white. 

 No gas or indol. Optimum reaction 



+15 to +18 Fuller's scale. T. D. P. 

 49-50°, 10 min. Opt. 28-30°. Aerobic 

 zymase, rennit or pepsin. 



It occurs as a pathogen on alfalfa and issues in clouds visible to 

 the naked eye from small pieces of tissue of the diseased stem or 

 leaf when mounted in water on the slide. These clouds under the 

 high power resolve into actively motile rods, relatively short and 

 thick. The bacteria are also found in practically pure culture in 

 the exudate which oozes from the diseased tissue as a clear viscous 

 liquid and collects in drops or spreads over the stem. Sackett 

 with pure culture inoculations produced the typical disease and 

 re-isolated the organism with unchanged characters. Re-inoculated 



Fig. 15. — Ps. malvacearum. 

 Early stage of stomatal infec- 

 tion in angular leaf-spot of 

 cotton. After Smith. 



No diastase, invertase. 



