Ethel M. Doidge 01 



dropped, but not in any of the tubes planted with the proboscis or 

 mandibles alone. 



Artificial infections were readily produced with the culture isolated 

 from the bee traces. 



It seems possible that ants may also be partly responsible for carry- 

 ing infections, as quite a number of them were noticed working in the 

 infected flowers at one farm in the Stellenbosch District. 



Etiology. 



When the organism causing the bacterial blight in pear blossoms 

 was first isolated in October 1915, the blossoming season in Pretoria 

 was almost at an end, but a preliminary infection experiment was carried 

 out with the few flowers which were still to be found on the trees. The 

 blossoms sent from Stellenbosch were shrivelled and quite black, but 

 bacteria were very plentiful in the tissues and no difficulty was ex- 

 perienced in obtaining a pure culture. 



The weather w^as exceedingly hot and dry so that it was useless to 

 attempt any inoculations in the orchard. A number of twigs bearing 

 apple and pear blossoms were therefore carefully cut under water, and 

 conveyed to the laboratory where they were covered over with bell 

 jars; some of these were atomised with a suspension of a culture in 

 sterile distilled water, others kept as controls. The latter remained 

 fresh and showed no signs of drooping or discoloration during the 

 experiment. The inoculated blossoms, however, showed water-soaked 

 spots on the petals, calyx, and peduncle after 24 hours; in 48 hours 

 these had become very numerous and began to turn brown, and in a few 

 days the whole flower had turned black and fallen. 



The organism was readily re-isolated and inoculated into some young 

 pears by atomising as before; a few infections were thus obtained in 

 pearlets which had just set, but not on the fruit of the size of a walnut 

 or larger; that is to say, the organism seemed unable to attack the 

 young fruit after it had begun to harden. 



After visiting the affected orchards in September, 1916, fresh 

 cultures were obtained from material collected, and a number of inocu- 

 lations were carried out with the organism thus freshly isolated, the 

 strain isolated the previous year and with Barker and Grove's organism. 

 Inoculations were carried out in one of three ways ; the flower was in- 

 fected by touching the receptacle with a platinum needle, which had been 

 charged with a small quantity of agar culture ; a drop of a suspension 

 of an agar culture was placed on the receptacle with a fine pipette; 



