5i8 DISEASES OF CULTIVATED PLANTS 



This disease is said not to be identical with the American 

 pear blight, due to Bacillus amylovorus. 



Aderhold and Ruhland, Sond. Arb. d. Kais. BioL Anst. 

 fur Land. u. Forstu., 5 (1907). 



Stem rot or blackleg of tobacco. This disease of tobacco 

 is well known and widely distributed in Japan. It is caused 

 by Bacillus nicotianae (Uyeda). The symptoms of its presence 

 are, yellowing of the leaves, blackening of the stem, and finally 

 the complete destruction of the root. The symptoms thus 

 are somewhat similar to those caused in the tomato by Bacillus 

 solanacearum. 



The organism is rod-shaped, ends rounded and ciliate, 

 1-1*5 Xo'5-o'7 p. Differs from B. solanacearum in physio- 

 logical and morphological points. Infection takes place 

 through the root-hairs, through stomata or wounds. Dampness 

 and a high temperature favours the disease. 



Acid manures check the bacillus when present in the soil. 

 Alkaline manures do not. 



Uyeda, Y., Bull. Imp. Cent. Expt. Sta. Japan, i. p. i 



Blight canker of apple-trees. This is due to the same 

 organism (Bacillus amylovorus, de Toni) that causes pear 

 blight. It attacks trees of any age, but is most destructive to 

 trees just coming into bearing. Canker spots appear as dis- 

 coloured and somewhat sunken areas, the advancing margin 

 being usually slightly raised and blistered. On damp, cloudy 

 days drops of a cloudy, milky fluid exude from cankered 

 tissues through the lenticels or pores in the bark. Soon the 

 diseased tissue turns brown and dies. Such patches are well 

 defined by a crack along the line where the diseased tissue 

 has separated from the healthy bark. The progress of canker 

 is favoured by a humid atmosphere and cloudy days, and is 

 checked abruptly by bright sunny weather. Many cankers 

 are active for one season only and do but little harm, others, 

 however, continue for a succession of seasons, girdling the 

 branch or trunk as the case may be, and finally killing the 

 tree. Canker spots vary in diameter from half an inch 

 upwards; some are a foot or more in length and several inches 

 across. On vigorous trees they are small and circular in 

 outline, and form funnel-shaped wounds in the wood ; these 

 do not seriously injure the tree directly, but facilitate the 



