494 MICROBIAL DISEASES OF PLANTS. 



METHOD OF INFECTION. Under field conditions the causal organism 

 which, presumably, lives in the soil, enters the plants early in the growing 

 season with soil through stems which are cracked and split by late freez- 

 ing. In some instances, inoculation appears to take place by stomatal and 

 water pore infections. 



CAUSAL ORGANISM.- The writer has given the name Ps. medicaginis to the causal 

 organism, the characteristics of which are as follows: It is a short rod with rounded 

 ends, about i.2/t to 2.4/1 by o. 5/1 to 0.8/1 the majority being 2.iju by 0.7/1. It is 

 actively motile by i to 4 bi-polar flagella; non-spore forming and non-capsule forming. 

 Filament formation occurs frequently. The organism stains readily with the aqueous 

 stains, but is Gram-negative. 



It produces a surface pellicle on broth. Shining, grayish white on nutrient agar, 

 becomes fluorescent green after three days. Gelatin stab, surface growth only, and no 

 liquefaction. Potato discolored, moderate growth, cream to light orange yellow, 

 starch not destroyed. No growth in Cohn's solution. Good growth in Uschinsky's solu- 

 tion. Plain milk shows no change. Litmus milk becomes bluer after seven days, no 

 curd and no peptonization in thirty days. No indol. No hydrogen sulphide. Am- 

 monia produced from asparagin solution, Dunham's solution and nutrient broth, but 

 not from nitrate broth. Nitrates not reduced. No gas and no acid from dextrose, etc. 

 Obligative aerobe. Optimum temperature 28; no growth at 37.5. Thermal death- 

 point 49.0 to 50.0. Habitat, soil. Pathogenic for alfalfa (Medicago saliva). 



CONTROL. The only practical way of combating and controlling the 

 blight is by the introduction of resistant varieties, but no entirely 

 resistant strain has been obtained up to the present time. 



As a means of control, the writer recommends that the frosted al- 

 falfa be clipped, as soon as there is reasonable certainty that danger from 

 late frosts is past. This will rid the plants of the diseased portions, 

 and afford an opportunity for the early growth of a new cutting. If 

 this is done in time, the regular number of cuttings should be secured 

 with little or no loss in tonnage. 



BACTERIOSIS OF BEANS. 

 Pseudomonas phaseoli Erw. Smith. 



Frequently the foliage, stems, and pods of the common beans, as 

 well as the Lima bean are attacked by a bacterial disease. 



SYMPTOMS. The pods and leaves seem to furnish the best food supply 

 for the microorganism, and it is here that we find the most typical lesions 

 developing. Small, reddish spots appear which increase rapidly in size 

 and develop into watery, amber-colored blisters, surrounded by a pink 



