FIRE-BLIGHT OF APPLE, PEAR, ETC.: SIGNS 381 



leaves. Learn the appearance of " hold-over blight." Usually 

 on smooth trunks such patches may be detected readily by the 

 practised eye in the absence of the exudate since their color is 

 somewhat different from that of the normal bark redder, 

 browner. Under rough bark detection is more difficult and a 

 gouge should be used. Is the dark color of the blighted leaves 

 and shoots a bacterial stain or a host reaction? Kill leafy pear 

 shoots in various ways and see what results follow in the leaves. 

 To what extent are the roots attacked? Write a description of 

 the disease. 



FIG. 294. Buried and surface colonies of Bacillus amylovorus after 3 days at 

 21C. on +10 peptone beef gelatin. The bulk of the surface colony is floating 

 in the middle of a pit of liquefaction. Isolated from apple in 1915. Photographed 

 by the writer. X 7. 



Histology. How many centimeters in advance of visible 

 blight can the bacteria be traced down the blighting shoot? 

 What does this teach you relative to pruning for removal of the 

 disease? Is the organism motile in the tissues? Is the wood 

 attacked or only the bark? To determine this, examine in 

 various places from the soft extremity of the blighted shoot 

 downward. Any differences (compare with No. XI) ? O Gara, 

 who has had much experience, states that the bacteria may 

 occur in the rich sap wood of the Bartlett, Howell, and other 

 pears and in that of the Spitzenberg apple. According to 

 Reimer this apple is no longer planted in South Oregon because 

 of its great susceptibility to blight. When the bark only is 



