CEOWN-GALL AND SAECOMA. 3 



in many other plant diseases) they ought to be readily visible either 

 stained or unstained, for, quite unlike the cells, these spaces are free of 

 all confusing granular matters. By the doctrine of exclusion, there- 

 fore, the bacteria must be within the cells. The discovery of them in 

 place is complicated by the fact that they are not very numerous, are 

 not acid fast, are probably often in the form of involution cells or in 

 some other form difficult to identify, and are mixed in with numerous 

 minute crystals, crystalloids, and other granules of the host proto- 

 plasm, which itself takes bacterial stains readily. 



TUMOR STRANDS. 



In many instances (we can not yet affirm in all) the secondary 

 tumors are connected with the primary tumor by a deep-seated strand 

 or pedicel of tumor tissue. This strand wedges its way through the 

 interior of stems and leaves, after the manner of a foreign tody, 

 until in some suitable place, often at a considerable distance from the 

 primary tumor, it gives rise to a deep secondary tumor, which sub- 

 sequently ruptures through to the surface of the plant. This off- 

 shoot from the primary tumor occurs deep in the wood, at the junc- 

 tion of wood and pith, and may sometimes be seen with the naked 

 eye, owing to the fact that the chloroplasts in its cells become more 

 numerous than elsewhere and give to the strand a deep-green color 

 and because being under great pressure it wells out on cross section 

 of the stem, something like a cut muscle; at other times the strand is 

 restricted to a few cells and can be made out with difficulty even 

 under the microscope, but wherever it occurs in any quantity it is 

 seen to be totally distinct in its structure from the normal tissues 

 surrounding it, conforming to the tumor tissue in its histolog}'^, and 

 can be traced in the one direction to the primary tumor and in the 

 other to the secondary, and frequently in the course of its progress 

 from the primary to the secondary tumor we have observed island- 

 like enlargements, and comparison of these in various stages of de- 

 velopment show that they are the beginnings of other tumors. Some- 

 times these enlargements of the green strand have progressed far 

 enough to push up the normal tissues and show as a swelling on the 

 outside of the stem; at other times not. Finally, from this strand 

 we have cultivated out Bacterium tumefaciens^ and reproduced the 

 disease with the cultures. Frequently the wood in this part of the 

 stem takes on an increased groAvth. 



SECONDARY TUMORS HAVE THE STRUCTURE OF THE PARENT TUMOR. 



As might be expected from statements under the previous heading, 

 " Tumor strands," when the primary tumor occurs on the stem and 

 secondary tumors subsequently appear in the leaves the structure of 



[Cir. 85] 



