14 



f uchsin and gentian violet, and reminded one of a very thick, resistant, 

 slightly branched mycelium (figs. 2 and 5, and PL II, fig. 4). In the 

 later stages it was found to break up, the pieces remaining for some 

 time between the cells (fig. 2). This was later shown to be the sub- 

 stance left by aphides in puncturing the tissues, and will be described 

 more in detail farther on. Nothing of this kind was found in the form 

 of the disease characterized by the minute spots, which do not increase 

 much in size, or in the elongated spots with irregular outlines. 



The only bodies in the diseased cells that might be mistaken for 



Fig. 1.— Cross section through a fully developed spot in a mature carnation leaf, the section being 

 cut a little to one side of the lines of puncture. The diseased cells are greatly enlarged and have 

 lost most of their chloroplasts. (Drawn with Zeiss camera lucida, x 264 diameters.) 



bacteria were small proteid granules, resembling proteosomes, which 

 stained with difficulty, swelled up, and lost their shape in 5 per cent pot- 

 ash. The chloroplasts of the diseased cells either do not develop at 

 all or after having lost their color shrink to about half their normal 

 size, and, like the proteosomes, stain with difficulty. 



The microscopical examination therefore indicated that the disease 

 could not be attributed to bacteria, for had these been present in the 

 cells in considerable numbers they would have been readily detected, 

 especially in the stained material. 



