10 EFFECT OF BLACK EOT ON TURNIPS. 



is the less to be regretted, however, since we may confident!}' expect 

 this phase of the subject to be treated very fully and satisfactorily'^ iu 

 the forthcoming papers of Jones and Potter/' 



GENERAL CONSIDERATIONS. 



So far as I can determine from sections, Ps. camjyestris is capalile 

 not only of destroving the middle lauiella. but also of dissolving the 

 cell wall proper. This it does slowly. At fi.rst I thought that I 

 detected a swelling of the walls prior to their disappearance, but sub- 

 sequent comparatiA'e measurements of the walls supposed to be swollen 

 w4th normal walls left me in doubt. Fresh material, which has not 

 been examined to this end, might give a ver}^ difi^erent result. That 

 the solution of the cell walls is progressive is shown b}'^ the fact that 

 many of the walls still remaining in the bacterial masses are only one- 

 third to one-fourth as thick as the walls of adjacent uninjured cells. 

 In certain cases where the bacterial mass lies up against the wall of a 

 cell on one side and not on the other, there has been a distinct thinning 

 of the wall on the side next to the bacteria. The difficulty of makii g 

 exact determinations is increased by the considerable variability in 

 thickness of the walls in the normal parts of the plant. 



Kussow's cellulose test gave ver}^ distinct pictures of the gradual 

 solution and final disappearance of the cell wall. The uninjured cell 

 walls gave a blue reaction, those in process of solution stained feeblj^ 

 or not at all. Sections were also stained in carbol fuchsin, picro- 

 nigrosin, iron htiematoxj'lin, and Fleming's triple stain. The vessels 

 of the root are distinguished very readil}- from the other parts of the 

 root by the safranin of the triple stain, which picks out the lignified 

 reticulations. The bacteria are stained well by carbol fuchsin, by 

 iron ha^matoxylin, and by nigrosin. 



The closed bacterial cavities in this root vary in size from openings 

 involving onl}^ two or three adjacent cells to spaces formed by the 

 destruction of hundreds, even thousands, of cells. They are full of 

 bacteria when not so exposed that the latter have difl'used out into the 

 alcohol. 



In many cases parenchyma cells are squeezed together from without 

 and the bacteria do not enter them until they are crushed out of all 



« Since this was written Mr. Potter's paper has been published. He finds that 

 individual bacteria of Pa. destructans hore small holes through membranes previously 

 softened by an enzyme, and in this way enter the cells. Such observations are of 

 course enormously complicated by the minuteness and abundance of the bacteria, 

 and one must be on guard against appearances, which are often deceptive, particu- 

 larly with dry lenses. Potter's statements, however, are positive, and are based on a 

 number of observations with l)oth fresh and fixed stained material, so that for the 

 present, and so far at least as regards the species in ciuestion, we may accept his 

 statements as substantially correct. They will probably soon be verified or contra- 

 dicted by other observers. 



