592 MICROBIAL DISEASES OF PLANTS 



Method ot iNrECTioN.— ^Under field conditions the causal organ- 

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

 growing season with soil through stems which are cracked and spHt by 

 late freezing. In some instances, inoculation appears to take place by 

 stomatal and water pore infections. 



Cattsal 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 11.2/ito 2.4/4 by o.S/t to 0.8/1 the majority being 2.1/t by o.^jit. 

 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 aqueoiis 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, 

 starph not destroyed. No growth in Cohn's solution. Good growth in Uschinsky's 

 solution. Plain milk shows no change. Litmus milk becomes bluer after seven 

 days, no curd and no peptonization in thirty days. No indol. No hydrogen sul- 

 phide. Ammonia 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.S''- Thermal death-point 49.6° to 50-0°. Habitat, soil. Pathogenic 

 for alfalfa {Medicago sativd). 



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, although the 

 Grimm alfalfa is practically free from it. 



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 por- 

 tions, and afiford 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. 



Bactekiosis 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 



