340 PROCEEDINGS OP THE ACADEMY OP [1886. 



It was early observed by cultivators, being recorded by Coxe, 

 that succulent shoots blight the most readily, and any process of 

 cultivation which as far as possible prevents succulency has 

 always been considered an aid in keeping the disease in check. 

 The avidity of the blight bacteria for water has been well demon- 

 strated in the cultures on slices of pears. There seems to be 

 some connection between these facts and the well-known fact 

 that the disease shows different degrees of virulence in different 

 varieties of fruit trees, especially in different varieties of the 

 pear. The variation, or at least part of it, to be observed in 

 pears, apples, quinces, hawthorns, etc., may be due to some inhe- 

 rent difference in the nature of the host, not readily formulated ; 

 for we find that the blight bacteria will grow to only a slight 

 extent in the succulent peach shoots, and not at all in most 

 other plants.^ But in varieties of the same fruit it may reason- 

 ably be inferred that to a considerable extent the difference in 

 the progress of the disease is due to physical causes. 



To determine what relation the hydration of the tissues holds 

 to this question, a series of determinations of the percentage of 

 water in the parts of the tree most subject to blight has been 

 begun. These are yet incomplete, and can only now be referred 

 to briefly. 



The Bartlett and Seckel pears very well represent the extremes, 

 the first being most affected by the disease and the second least. 

 Twigs taken from the tree in February were found to contain 50'2 

 per cent, and 50"85 per cent, of water respectively. Twigs taken 

 in the same way April 30, bearing flower buds, but with the 

 leaves removed, gave 68"7 per cent, and 67*3 per cent, of water. 

 The half-grown fruit, taken the first week in July, gave '79*3 per 

 cent, of water for the Bartlett and 71 per cent, for the Seckel. 

 According to these figures the amount of water in the Bartlett 

 and Seckel twigs during the winter is practically the same, but 

 during growth both the twigs and fruit of the Bartlett contain 

 more water than those of the Seckel. These numbers give some 

 support to the view that succulency and the strength of the dis- 

 ease are directly related, but the data are yet too incomplete to 

 warrant a definite statement. 



1 Rep. N. Y. Agric. Exper. Station for 1884, pp. 362, 377 ; Amer. Nat., 

 vol. xix, 1885, p. 1182. 



