88 ~ EXPERIMENTAL FARMS 



PEAE AND APPLE BLIGHT. 



The disease variously known as "Apple blight," "Pear blight," "Twig blight" 

 and " Fire blight " has wrought a serious amount of injury to trees in the Ottawa 

 Valley during the past season. 



The presence of this disease has been noticed in America for 100 years past ; one of 

 the first observers being W. Denning, of Massachusetts, who published an article on 

 the " Decay of apple trees' which appeared in the Transactions of the Society for 

 the Promotion of Agriculture, for 1794. In this article he describes the disease as 

 attacking pears and quinces, and thinks that it was caused by a borer in the trunks 

 of the trees. Later we find mention of it in the writings of that pioneer in fruit 

 culture, Wm. Cox, in his work entitled, " The Cultivation of Fruit Trees," written 

 in 1817. Here it is called "Fire Blight," and is minutely described. He says: 

 " I have in twenty years lost upwards of fifty trees in the fulness of vigour; some- 

 times in the most open and airy situations, and in every kind of soil." 



In horticultural writings numerous references can be found with regard to this 

 disease, without absolutely divining or assigning the cause of it up to 1868, when 

 Dr. Hull, of Illinois, first attributed the disease to fungi. 



In 1877 the presence of bacteria in affected limbs was discovered by Prof. T. J. 

 Burrill, and in 1880 Prof. Burrill published the first authoritative account of the 

 bacterial origin of this disease, and cited in proof of his observations a lai-ge number 

 of experiments in transmitting the disease in various ways from one tree to another 

 by inoculation. A pertinent question at this time was whether bacteria themselves 

 caused the death of the aifected portion, or whether these followed as a natural con- 

 sequence in the track of the life destroyer. 



The experiments of Prof Burrill went largely to show that the bacteria them- 

 selves were the actual cause of death, and this point was satisfactorily demonstrated 

 by Prof. Arthur, then of the New York Experiment Station, in 1886, who proved 

 by careful experiments that the disease could only be transmitted by using the juices 

 of branches which contained the characteristic bacteria. In support of this position 

 Prof. Arthur makes the following statements : — 



A. " Bacteria are found in great abundance in actively blighting tissues, so as 

 to be demonstrable to the naked eye, and occur in less abundance in proportion as 

 the disease is less active." 



B. " The disease may be introduced into healthy tissues by inoculation with 

 germs from diseased tissues." 



C. " It is communicated with equal certainty when the germs are separated from 

 all accompanying juices of the diseased tissue, by a series of fractional cultures. 



D. " Per contra, it is not communicated by the juices of the disease after the 

 germs are removed by filtration. 



E. " Germs connected with the disease constitute a single species, which is essen- 

 tial to successful inoculation. 



F. " Per contra, the numerous species of earth, air, and water are found to a 

 noticeable extent in connection with the disease, and cannot be made to originate it 

 by inoculation or otherwise." 



Prof. Arthur further states as the result of his investigations that "A constant 

 ratio is found between the percentage of water in the branches of the several kinds 

 of pomaceous fruits, corresponding to some extent with their liability to blight. 

 The popular opinion that the more rapid growth of the shoots, the more succulent 

 their tissues, and therefore the more liable to blight, is thus confirmed by trial." 



The bacteria may keep alive in branches cut from the tree, and remaining in 

 water or moist ground till the following season, and they may also be cultivated in 

 solutions of garden soil, indicating the desirability of promptly destroying all 

 blighted limbs. 



With a view of obtaining information with regard to the spread and extent of 

 this disease in the Dominion, a circular was sent to the leading fruit growers in the 

 various provinces. The information obtained from these replies is contained in the 

 tables annexed. V 



