Fire Blight of Pears, Apples, Quinces, Etc. 157 



again, repeating this every half hour or so, as long as food, water and 

 proper warmth prevail. They do not travel through the sap tubes 

 of the plant, as is often supposed, but slowly work their way through 

 and between the cells of the bark, spreading thus into the healthy part 

 of the twig or limb, and kill it. They are able, even under the most 

 favorable conditions, to penetrate but a few inches a day. 



That these minute bacteria are the true and only cause of this disease 

 h^s been demonstrated many times. Dr. T. J. Burrill ('81), Botanist 

 of the Illinois Experiment Station, who first discovered the true cause 

 of this disease, found, as have many investigators after him, that these 

 minute plants are always present in 

 great numbers in the blighted bark 

 even along the advancing margin of 

 the disease. He further found that 

 when these bacteria were introduced 

 by means of a needle into growing 

 fruits or the tips of growing shoots of 

 perfectly healthy trees, the character- 

 istic symptoms of the disease appeared 

 in about nine days; the inoculated 

 shoots blighted. This experiment has 

 been many times repeated by other 

 investigators and always with the 

 same result. Any grower may con- 

 vince himself on this point by making 



inoculations from a freshly blighted 



^ . . ^ 1 1^1 • u J. r Fig. 12. — Bacillus amylovorus, the 



twig mtO healthy, growmg shoots of bacteria that cause the Blight. Note 



pears or apples with a common needle. that they multiply by simply divid- 

 The inoculation should be made in the ^"^ tno w . 

 evening or on a rainy or cloudy day. As further proof that these 

 bacteria are the responsible agents, numerous investigators, including 

 the writers of this bulletin, have many times obtained the organisms 

 in pure cultures from diseased trees, grown them in beef broth, and by 

 inoculation with them from these cultures into healthy trees of apple, 

 pear and quince, have readily and uniformly produced the character- 

 istic blighting. There is no longer any question as to the cause of this 

 disease. 



These bacteria are carried from tree to tree and introduced into 

 blossoms or growing shoots by insects of various kinds (Fig. 13). Waite 



'81 Burrill, T. J. Blight of Pear and Apple Trees. 111., Ind. Univ. Rep. 



10:67. 



