56 A Bacterial Spot of Citrus 



they are 5 — 10 mm. in diameter and depressed 1 — 2 mm. below the 

 surface of the healthy rind. The spots are more or less round, but 

 when a number occur in close proximity to one another, they coalesce 

 and result in the formation of large irregular blotches (Plates III and IV). 



A close examination of the spot usually reveals a small wound in 

 the centre which has been the starting point of infection; in a few 

 cases a large diseased area showed numerous scratches, possibly the 

 result of sAvinging against a thorn in the high winds. 



Young infections vary considerably in colour; one spot, 28 mm. 

 in diameter, was maize yellow, the centre buckthorn brown, others 

 were chamois with margin and centre of Mikado brown. In a few 

 cases there were one or more concentric rings of brown on a lighter 

 ground. They become much darker with age, varying in colour from 

 Argus brown through light seal brown to blackish brown ; frequently 

 the dark central portion is surrounded by a reddish rim. 



It is not a soft rot, and the spots are either leathery in texture or 

 else quite hard. A number of affected lemons were kept for some days 

 in a moist chamber and at the end of that time, dirty yellowish drops 

 of a viscid substance were seen oozing from the point of infection. 

 A similar circumstance was observed in lemons artificially infected 

 and kept in a moist chamber. 



By cutting through the discoloured spots it can be seen that there 

 is a very definite line between the sound and the diseased tissues, in 

 some cases only about half the thickness of the rind is affected ; in 

 others the organism penetrates right through the rind and invades 

 the pulp. The pulp below the discoloured rind becomes rather dry 

 looking and has a peculiar taste and smell ; in severe cases it is dis- 

 coloured to a cinnamon brown, only the outer parts are affected and 

 the disease does not appear to spread in a tangential direction. 



On oranges the spots are slightly different in appearance; they 

 average 20 — 30 mm. in diameter and are not so deeply sunken as those 

 on the lemons ; the colour is usually buckthorn brown to Dresden 

 brown ; I have never observed spots on oranges with the conspicuous 

 almost black discoloration so common in lemons (Plate VIII). 



Naartjes become very badly infected: a number of naartjes sent 

 direct from the orchard shewed as many as 20 — 30 spots of varying 

 size on a single fruit, they were round to irregular and 1 — 25 mm. in 

 diameter ; slightly sunken and varying in colour from something 

 between Mikado and Sayal brown to blackish brown (Plate VII). In 

 some large spots with an evident thorn prick in the centre the disease 



