WALNUT r.ACTERIOSlS. 4I I 



consitlerable loss will probably be experienced in exceptionallv 

 \vet seasons, and, as has been observed in California, a grove may 

 he very bad one year and nearly free from disease the next. 



In districts like Oudtshoorn, wliere the rainfall is small and 

 mostly in winter, no serious trouble is to l)e expected, and fruit- 

 growers intending to plant walnuts in the more humid districts 

 would l)e well advised to obtain their trees from localities where 

 the disease is as yet imknown. 



The C)rgamsm. 



There can be no doubt that the organism causing walnut 

 bacteriosis in this country is identical with the Bacterium Jtig- 

 laiidis (Pierce) known in California. 



This organism has been repeatedly isolated from spotted 

 leaves and nuts, and in its cultural and morphological characters 

 agrees with those given by Pierce for Bactcriniji Jiiglaitdis. A 

 fev.- minor differences in the cultural characters have been 

 observed, but I do not propose to go into detail about these at 

 present, as I am making a comparative study of this organism and 

 Bacterium campcstris, which it closely resembles. 



Bacterium J it^i^hijidis develo])s rather slowly on culture media, 

 the colonies are just visible to the naked eye after 48 hours, as 

 minute whitish sjjecks ; they rapidly become vellow as they increase 

 in size. Xo difficulty was experienced in obtaining a pure culture 

 of the organism, and numerous infections were obtained by atom- 

 ising young walnut trees with a suspension of the culture. 



From the leaf infections thus obtained the organism was re- 

 isolated, and a second set of trees inoculated with positive results. 

 None of the controls became infected, 1 have had no opportunity 

 of infecting young nuts, but cultures obtained from the nuts 

 readily infected the leaves. 



The characteristics of the organism may be briefly sum- 

 marized as follows : — 



Morphology, a rod with rounded ends, usually single or in 

 pairs, 1.5 — 3 //. long by .3 — .5 u broad; no spores observed; motile 

 by means of a single polar flagellum. 



Cultural Characters. — On agar plates in 3 days develops 

 small yellow surface colonies, somewhat raised in the centre, these 

 increase in size with age ; submerged colonies, minute, lenticular : 

 grows well on potato and other vegetable cylinders, forming an 

 abundant, moist, shiny yellow growth ; liquefies gelatine slowly : 

 clouds beef bouillon, and forms a ring-like growth above the sur- 

 face of the medium ; in milk cultures it causes a separation of the 

 casein, which becomes solid ; the casein is gradually redissolved ; 

 slowly destroys starch, produces indol in peptone media. 



The thermal death point I have not yet determined; this 

 and other details will be published later in connection with the 

 comparative study already referred to, and which is not yet com- 

 plete. 



