BLIGHT. 127 



in a few years the whole East was infected. To prove how 

 rapidly this can be accomplished, I need only refer to the 

 recent introduction of the San Jos scale into New Jersey, and 

 elsewhere throughout the country. If a slow traveling fly and 

 insect could so quickly be scattered far and wide, what shall 

 we say or how limit the spread of the subtle bacteria ? Of 

 course, I am presuming that, once in the sap of a tree, they 

 remained there, often in numbers, perhaps, too limited, or 

 from want of proper conditions for development, unable to 

 produce the blight. The eastern states, the nursery grounds 

 at that time for the whole country, once thoroughly infected, 

 we see how almost of necessity the bacteria were rapidly 

 scattered in nursery stock from the Atlantic to the Pacific, 

 and the Lakes to the Gulf^of Mexico. That this infection did 

 actually occur all over the eastern half of our country is 

 proved by continuous developments of blight, from time to 

 time, in different localities throughout this whole region, fol- 

 lowing rapidly after its original appearance in the East. 



While, then, the presumption of the present existence of 

 these bacteria in all pear trees is a fair one, it is a known fact 

 that they do pervade the sap of all pear trees on which the 

 external evidences of blight have manifested themselves, fruit 

 growers having been repeatedly warned to cleanse their knives 

 and shears thoroughly after pruning diseased trees. Now, 

 then, admitting, as the authorities on this subject do, that the 

 sap of all such trees does contain the bacteria, the presump- 

 tion is that they remain there in greater or less numbers, and 

 the burden of proof is on them to show the contrary. 



We come, now, to the vital question : What are the 

 actual causes of, or rather conditions for, the visible mani- 

 festations of blight ? I stated in another place that tempera- 

 ture, moisture, and pruning in certain cases were at the 

 bottom of it, and foreshadowed in my supposed history of its 

 original appearance a theory, and the only one that will com- 

 pletely account for all the phenomena. And right here I 

 have to make an assertion, positively true, but quite as revo- 

 lutionary as that regarding the best form of a tree for plant- 

 ing, which is, that the universal statement that the "best 



