Ethel M. Doidge 53 



including the plum and apricot, and on numerous plants indigenous to 

 America. Of the varieties of Pear which was attacked, the Bartlett 

 is said to be very susceptible; other varieties are bracketed with the 

 Bartlett as susceptible, but there seems to be considerable divergence 

 of opinion on this point. The Keiffer, Duchess and Winter Nelis, and 

 the oriental group in general are more resistant. 



Sym])toms. 



Although infection most frequently takes place through the flowers, 

 the blossom blight is not by any means the most serious phase of this 

 disease. When the blossoms are attacked the receptacle becomes 

 blackened first, infection taking place through the nectaries, but the 

 infection rapidly spreads into the ovary and the flower stalk and invades 

 the twigs. The blossoms and leaves of affected twigs become dis- 

 coloured, turning light or dark brown, or sometimes red, and finally 

 shrivel up and die. The spread of infection is frequently so rapid as 

 to result in the complete blackening and death of all branches and 

 spurs upon which flower clusters have been borne. The blight may 

 continue to extend down the branch or twig, the branch being entirely 

 killed as it progresses, and in course of time it may extend into the 

 larger limbs. The bark of infected twigs and branches becomes blistered, 

 and on the blistered areas there is often found a gummy exudate 

 which is crowded with the rods of the causal organism; this exudate 

 attracts the insects which are responsible for the further spread of the 

 disease. Immature fruit is frequently attacked; it becomes light 

 brown and finally black, the flesh soft and pulpy, and the skin somewhat 

 wrinkled. Ripe fruit seldom becomes infected. 



The Characters of Bacillus amylovorus (Burr) de Toni. 



Morfhology. 



Bacillus amylovorus is a short rod with rounded ends, -9 — 1-5 /a 

 X •? — 1/x in dimensions, longer (nearly up to 3/x) and slightly narrower 

 in old cultures. 



It is motile by means of several (4 — 8) peritrichous flagella ; no 

 capsules or spores have been observed. The rods are usually single or 

 in pairs, but in young cultures short chains made up of 3 — 4 individuals 

 have been noted. 



The organism is Gram-positive. 



