1880.] 



MICROSCOPICAL JOURNAL. 



183 



of the liber. This organism is allied 

 to, if not specifically identical with, 

 the butyric vibrione of Pasteur, and 

 the Bacillus amylobacter of Yan- 

 tieghem. After referring to the 

 history of the disease in this country, 

 which goes back at least a century, 

 the experiments wliicli were made 

 with the specific poison or ferment, 

 in inoculating healthy trees, and in 

 other ways, were recounted in de- 

 tail. A"^ter it was determined that 

 a specific living organism, the Bacil- 

 lus^ was always present in the liber- 

 cells of the affected trees or bran- 

 ches, an isolated acre of ground, upon 

 which there were ninety-four pear 

 trees of different ages and varieties, 

 was selected for the experiments. On e 

 method of experiment was to cut 

 off small portions of the bark of 

 diseased trees, and to insert them in 

 healthy trees. The results of these 

 experiments were given in a table, 

 which showed that a large percent- 

 age of the experiments were per- 

 fectly successful in communicating 

 the blight from the diseased tree to 

 the healthy. Sixty-three per cent, of 

 all the pear trees thus inoculated 

 became diseased. Of the pear trees 

 that were inoculated with the virus 

 from diseased pear trees, fifty-four 

 per cent, became affected ; of those 

 peartrees inoculated from blighting 

 apple trees, seventy-three per cent, re- 

 ceived the disease. When the poison 

 was taken from the pear trees, to 

 inoculate apple trees, the percent- 

 age of successful operations, was 

 much below that obtained when the 

 process was reversed, probably be- 

 cause the apple tree is the more 

 hardy of the two. The virus seems 

 to be quite harmless when it is ap- 

 plied to the epidermal surface of 

 the leaves of the tree ; it does not 

 seem to enter through the stomata. 

 Of the entire number of recorded 

 observations, 84.78 per cent, were 

 successful, while of the whole num- 



ber of inoculations with the knife, 

 52.07 per cent, were effective.. The 

 organism to which the disease is at- 

 tributed is so minute that a strong 

 magnifying power is necessary to 

 enable one to study it, or to make 

 out its form. It assumes various 

 shapes during its development, and 

 these different f oi'ms may usually be 

 seen at one view in the microscope. 

 The characteristic form is that of 

 two oblong joints with rounded ends. 

 Their transverse diameter is about 

 _()02"i'»,, and the length of each 

 joint about .OOS'"'"- They are 

 comparatively shorter and thicker 

 than the common Bacterium termo, 

 and they move less rapidly. If this 

 should prove to be the organism 

 which is the well-known agent in 

 converting starch, sugar, etc., into 

 butyric acid, hydrogen and carbon 

 dioxide, this would not invalidate 

 the assumption that it is the cause 

 of the disease, but it might render 

 the discovery of remedial treatment 

 less hopeful. The most conspicuous 

 change in the tissues of the affected 

 plants revealed by the microscope is 

 the almost total disappearance of 

 starch from the cells. 



Dry Mounts.* 



BY PROFESSOR H. L. SMITH. 



The very simplicity of this pro- 

 cess causes me to wonder why it 

 was not thought of before. I take 

 a sheet of thin writing paper, white 

 or colored, and dip it into thick 

 shellac varnish (shellac dissolved in 

 alcohol), and hang it up to drv. 

 When thoroughly dry it should 

 have a good glaze of the varnish on 

 it (different thickness of paper can 

 be used according to depth of cell 

 required). Out of this shellac 

 paper I cut my rings, and these can 



♦Abstract from an article published in 

 Science. 



