458 MISSOURI STATE HORTICULTURAL SOCIETY. 



with the young and succulent growth. After the bark and outer por- 

 tion of the branch are blackened with the disease, the sap of the tree 

 ■continues to pass through the center of the limb for a time ; hence the 

 prolongation of life in the leaves and ends of the branch. Blight can 

 be propagated only by natural processes ; tying afiected branches in 

 healthy trees failed to impart the disease. It lives in the branch 

 through the winter. Disease germs enter the tree through the ten- 

 ■derest tissues at the ends of the branches and in the flowers, usually in 

 early spring, but where they come from is yet a mystery. Germs will 

 grow in perfectly dead matter of almost any kind, especially in any 

 •starchy or analogous substances. A particle of blighted pear twig 

 placed in a solution of corn meal and water, boiled, would fill the 

 liquid with germs in a day or two. The course of the disease is usually 

 about as follows : 



" The germs in a diseased tree escape to the surface in a sticky 

 •exudation ; washed free by rains, they drop to the ground, and multi- 

 plying indefinitely in decaying vegetable substances, either beneath 

 the trees, or in marshy or wet places at a distance. Here they may 

 pass the winter and even live for years. They are borne in the air, 

 when dry, by the wind, or carried up by evaporation. Then, coming 

 in contact with the moist surface of tender twigs or the center of the 

 flower, the germs find entrance to the tree, and thus the reproductive 

 process goes on. We have proved absolutely that the germs only cause 

 the pear blight, and, further, that the germs are of a specific kind." 



The scientific name of the specific bacteria, which produces the 

 pear blight, he said, is Micrococus amylororus. The pear tree is espe- 

 cially liable to blight by reason of its succulent habit of growth. 

 Apple trees, being of more solid growth, are not usually attacked or 

 injured to any great extent. 



Various pertinent questions were asked by different members at 

 the close of the Professor's instructive paper, but he was unable to 

 give any very conclusive answers. For instance, in replying to the 

 question, "What shall we do to prevent the pear blight?" he said: 

 *'While I was studying the disease, half my orchard blighted before I 

 knew it. I know of no remedy so far. An antiseptic over the grow- 

 ing shoots, if it could be kf^pt there, would, of course, protect them, 

 but the rains would wash it off." 



Mr. Moody had used sulphur and lime for some years past, and had 

 not been troubled with blight during the last five years, in an orchard 

 •of 10,000 trees ; but Prof. Arthur has no faith in it as a preventive. In 

 his opinion, no washes or applications to the soil can have any influ- 

 ence upon the blight. "Do not fertilize heavily ; don't let the trees 



