2/8 THE CULTIVATION OF THE 



summer, we should have had the story of the Pear- 

 Blight of every kind in a nut shell. We take the 

 healthy Pear tree. In this tree there are bacteria, as 

 there are in all healthy trees. Now, for some of the 

 reasons mentioned, perhaps, or for others, these bacteria 

 increase, millions and millions and thousands of millions, 

 in a few hours. Now follows a great stirring up, a fermen- 

 tation ; heat is increased, and the sap, instead of being 

 good, rich, healthy blood for the tree, is hot, with the 

 fever produced by the presence of these disease-germs, 

 for such they now are. The digestion of the tree, the 

 changing of starch into sugar, the action of the 

 chlorine on the leaves, etc., is all interfered with, and 

 for reasons of their own, these bacteria congregate in 

 one limb or two limbs, (just as in man, under similar 

 circumstances, one toe only may become gangrenous,) 

 and congregating here, the attacks are so fierce and 

 concentrated, that all molecular change is checked, and 

 hence, with this stoppage of cell-action comes gangrene, 

 death. In a healthy tree these germs probably assist 

 the change of starch to sugar, and only are pests when 

 increasing rapidly and infinitesimally as they do in 

 diseases of animals or vegetables. In Peach-Yellows 

 there are enough to sicken the tree, in Pear-Blight they 

 come in sufficient numbers to overwhelm and destroy 

 at once, and appear elective as to their choice of location, 

 not distributing themselves over the whole tree, but select 



