BOTANICAL GAZETTE. 272 



plant, whatever may be the indirect surroundings and conditions ren- 

 dering such operations possible. The experiments of last year have 

 been repeated and verified during the present season ( 1881 ), and further 

 research has shown that fruit trees are in no wise peculiar in this re- 

 spect. Many other plants suffer in a similar manner from the same 

 cause. Among trees, none are more certainly and surely destroyed in 

 this way than the Lombardy poplar, whose dead or dying spires so 

 commonly attract the attention of the most casual observers through- 

 out our land. Popidus trcmuloidcs dies snll more apparently like the 

 pear tree. The butternut and the linden succumb to the same dc- 

 .'^troyer. Ash and elm trees do not fully escape; the maples, especi- 

 ally the "sugar tree," often similarly suffer. Shrubs and herbaceous 

 plants are also injured or killed outright by the avaricious, omnivor- 

 ous little creatures. The leaves of the white flowered lilac wither up- 

 on their stems before they have half filled their proper duties, and 

 those of the common pa^ony die while the summer's sun invites them 

 to fuller development and activity. 



In these and many other instances, the destroying agent is almost 

 surely one and the same, though the appearance and even character- 

 istics differ very much in the resulting effects upon different subjects. 

 The pear tree more commonly becomes diseased throughout the entire 

 stem and its appendages, while the young twigs of the apple tree often 

 alone perish or a limited area of the bark upon the trunk dies. In 

 the lilac it is the leaves which suffer, the branchlets bearing them con- 

 tinuing in perfect health. In the case of the Lombardy poplar the 

 small limbs perish only because the larger parts are destroyed. So far 

 as I have observed, the leaves are not at all infected. If the yellows 

 of the peach is really due to the same specific Bacterium, a still further 

 difference is shown, for this tree does not die by inches, the disease be- 

 ginning in some well-defined place, and gradually si)reading. as in the 

 other cases. The whole top languishes, and it has been supposed that 

 the roots were also involved. My studies upon this disease have been 

 confined to severed s};ecimens sent to me through the mail, but in no 

 instance have 1 found the pieces of roots taken from diseased trees in- 

 fected with bacteria ; the diseased limbs always are. In the pear, ap- 

 ple, po])lar, etc., the roots are never the seat of the disease, and become 

 infected, if at all, only through the contagion from the trunk. 



Inoculations with fresh material (bacteria) are as certain to com- 

 municate the disease as are similar operations upon animals. Vaccin- 

 ation as practiced against small-pox is not successful in a greater num- 

 ber of instances than is this method of producing blight. In last 

 year's experiments sixty three per cent, of the total number of inocu- 

 lations in pear and apple unmistakably communicated the disease. 

 By operating on what became known as the most susceptible parts 

 and kinds, a much greater per cent, succeeded, approaching near to 

 one hundred. Similar punctures with a clean needle had no effect 

 whatever. Application to the outside of the unbroken epidermis was 

 ineffectual. These results are corroborated by similar experiments this 

 year, not however prosecuted to the same extent. 



Tliere are to my mind many interesting questions left unsolved, 



