THE FUNGI WHICH CAUSE PLANT DISEASE 27 



Ps. dianthi Arth. & Boll.^' Though originally reported as the 

 probable cause of carnation leaf spot, this organism is now regarded 

 as a saprophsrte. 



Ps. fluorescens (FlUgge) Mig. Straight and curved rods of 

 medium size in chains of two or several members. Cells 0.68 x 

 1.17-1.86 n. Spores not seen. Flagella 3>-6 polar. 



Gelatine liquefied; surrounding medium colored greenish-yellow; 

 Gram negative. Milk not coagulated. Indol weak. Bouillon, 

 turbid, fluorescent. 



This organism or two varieties of it are by Barlow *^ held re- 

 sponsible for a decay of celery. The organism was found in large 

 numbers in the decayed tissue; was isolated and typical rot was 

 induced by inoculation of pure cultures upon sterilized celery 

 stems. 



It is also credited with two distinct types of tobacco disease in 

 France, one of them on seed, the other on the growing plant. 

 Recently Griffon " has claimed that both of the varieties, Ps. 

 fluorescens liquefaciens and Ps. putrida are capable of producing 

 wet rot of various vegetables, carrots, rutabagas, tobacco, toma- 

 toes, melons, and that the latter organism is identical with Ps. 

 seruginosus. It is also held that B. brassicaevorus and B. cauli- 

 vorus are forms of Ps. fluorescens. 



Ps. fluorescens exitiosus v. Hall is said by van Hall *" to cause 

 rot of Iris. 



Ps. hyacinth! (Wak.) E. F. Sm., is a serious pest of hyacinths in 

 the Netherlands but has not yet been recorded in America.^' 

 It is medium sized rod with rounded ends, 

 measuring in the host 0.8-1.2 x 0.4-0.6 n; 

 actively motile by one long polar flagellum; 

 non sporiferous; liquefies gelatine slowly; 

 aerobic; no gas. It produces indol. Does not Fio. 14.— Ps. hyacinthi. 

 grow at 37°. Opt. 28 to 30°, T. D. P. 10 ^^^' ^°^*^- 

 min., 47.5°. It is a wound .parasite which grows in the vessels 

 forming a bright yellow slime and is closely related to Ps. cam- 

 pestris and Ps. phaseoli. 



Ps. iridis V. Hall ™ is described by van Hall as the cause of 

 decay of shoots and rhizomes of Iris. 



Ps. juglandis Pierce. (Group number -11. 51-.) *^ A rod 



3% 



