7<^ i'kliSIUKNTlAL ADDRESS- — SECTION C. 



Such cases, however, are exceptional, and the diseases 

 usually manifests itself in from one to three weeks. 



S'i' M I" TOM ATOLO(iY. 



I he macroscopic appearance of plants affected with hac- 

 tcrial diseases is not particularly characteristic, and cannot be 

 said to differ materially from that of plants attacked by fungi; 

 except in one or two cases where the symptoms are quite peculiar, 

 it is impossible to state the cause of the disease without a micro- 

 scopic examination of the tissues. 



One of the most common symptoms of disease is the forma- 

 tion of discoloured spots on' the leaves; these are at first dark 

 green, and oily or water-soaked in appearance, but subsequently 

 become brown or black. This is the case in almost all the so- 

 called leaf -spot diseases (mango and mulberry blight, angular 

 leaf spot of cotton, etc.), and, in most of these, similar dis- 

 coloured areas are the result of fruit and twig infections. When 

 the brown spots are numerous, the leaf or fruit frequently 

 yellows and falls prematurely. In other cases, deep red or even 

 purple-coloured spots indicate the presence of a leaf i^arasite ; 

 this is especially characteristic in the bacterial blight of Johnson 

 grass, Andropogon sorghum, caused by Bacillus sorghi. This 

 red or purple coloration is often noted in the early stages of the 

 shot hole disease of the peach or plum caused by B. pntni; in 

 the later stages the leaves show the circular or irregular perfora- 

 tions which give the disease its name. 



In other leaf-spots the leaf green persists in the neigh- 

 bourhood of the spot, while the rest of the leaf becomes yellow 

 (bean leaf spot). The staminate inflorescence of maize attacked 

 by Bacterium Stewarti ripens prematurely and becomes white. 



Discoloured areas on shoots, as the branch grows older, 

 frequently lead to the formation of extended open wounds or 

 cankers, which are elongated in the direction of the axis of the 

 branch. 



The black rot of cruciferous plants is characterised by a 

 blackening of the veins of the leaves, and a subsequent yellowing 

 of the areas of the blade affected ; a discoloration of the stem is 

 fiequently observed in plants attacked by Bacterium solana- 

 ccarimi. 



A sudden wilting of a j^lant which can not be explained by 

 dry conditions of soil or air may often be traced to the action of 

 bacteria, e.g., the cucumber wilt or the wilt of potato, tomato 

 and other plants. When seedlings exhibit this symptom it is 

 not infrequently the result of planting contaminated seed ; in 

 such cases the organism attacks the hypocotyl, and the young 

 plant quickly succumbs. 



In some diseases, the death of parts of the plant — leaves, 

 twigs or flowers — is the first symptom that is observed. In the 

 fireblight of pears and apples, the young terminal twigs with 

 their leaves and flowers are killed, and even large branches are 



