328 The Microscope. 



the leaf. If a leaf is previously marked ofP by ink-line into equal 

 areas, say two inches wide, and, upon alternate blocks is painted, in 

 one case a fluid containing the Bacillus described, and upon the 

 others, a sterile fluid of similar kind, the results are very striking 

 and convincing. We find the former, set speckled throughout with 

 the red dots. At a later time, say four days, the peculiar 

 checked appearance of the leaf coiTesponding to the treatment 

 named is conspicuously manifest, though not all of the tiny red dots 

 subsequently enlarge. The infected surface becomes irregularly 

 blotched. If now a portion of such a diseased leaf is slightly 

 flamed, then cut with a flamed knife, so as to divide the epidermis 

 and start a crack in the tissues, when the leaf is bent, a freshly 

 broken exposure of the diseased parts can be secured. A glass 

 pipette just from the flame can now be thrust into the newly-exposed 

 reddish tissues, and a culture started with pretty strong presump- 

 tions that whatever growth results, comes from the infected leaf. In 

 this manner, time after time, a piu'e culture of the specific Bacillus 

 has been secured, and from these cultures the disease has been again 

 started. Moreover, the Bacillus itself has been found numerously 

 enough in the affected tissues, both when the disease occurred spon- 

 taneously, that is naturally, and when artificially started, as described. 



But I have not yet learned to exhibit satisfactorily bacteria in 

 situ with vegetable tissues. No stain or method of decolorizing has 

 been found serviceable in these cases. Then, too, the sections must 

 be so thin that the cells themselves are usually cut and the contents 

 escape. If infiltrated the mass interferes,, or, if the latter is dissolved 

 the organisms are likely to be washed away. 



If sections are made of a newly-infected leaf, it is easy again to 

 demonstrate that the disease starts at the stomates. The guard cells 

 themselves may or may not be changed, but the cells immediately 

 beneath the aerial cavity show the initial influence of the disease. 

 From the stomates the injuries spread downward and sidewise. In 

 thus spreading, originally distinct s}>ots coallesce and form continu- 

 ous blotches, as described. 



The cell-walls are in no wise altered, so far as can be made out 

 by microscopical examination, except that they are stained through- 

 out with red instead of their normal clear white. The first change 

 observed in the cell-contents is a shrinking of the protoplasm, as 

 when treated with alcohol. It separates from the wall of the cell, 

 and appears rigid instead of the usual plastic consistence in health. 

 The chlorophyll granules, if present, lose their green color and break 



