CAUSE AND NATURE OF CROWN-GALL 



47 



If a thin section of a young gall be placed in water on a slide 

 and Flemmiug be allowed to gradually work under the cover- 

 glass, certain cells immediately begin to darken, and the whole 

 or a portion of the contents appears in the form of spheroidal 

 bodies. This appearance of dark spheroidal bodies under the 

 action of Flemming is not observed in healthy tissue, and is 

 thought to occur only in cells containing the parasite. Fig. 25 

 is a photo-micrograph of a thin section showing the position of 

 certain cells darkened by 



the Flemmiug. The dark 

 masses which appear to 

 completely fill the cells 

 are in reality dense ag- 

 gregations of globular 

 bodies. 



It has been observed 

 that the plasma of certain 

 slime-molds in the plas- 

 modial stage collects into 

 small globular masses 

 when about to die. 40 It 

 is possible that the action 



r ■ -r-»i • i.1 • Fisr. 2s. — Photo-micrograph of a thin section 



Of Flemming OII this Or- sh J ing 5 the position of ' Certain cells having their 



ganisill induces a similar contents darkened by the action of Flemming. 



t, ( X 360. ) 



phenomenon. J 



A satisfactorily fixed and stained section, when viewed with 

 an objective of sufficiently high power, shows certain cells, 

 usually adjacent to the meristematic tissue, more or less filled 

 with frothy, vacuolar protoplasm, as previously described. The 

 cell contents, however, now stands out clearly and well defined, 

 and the protoplasm frequently appears as a close network of 

 cytoplasmic strands completely or nearly filling the cell (see 

 Plate). This condition is the first evidence of the parasite in 

 the cell, but the plasma is so intimately associated with the 

 cytoplasm of the cell that thus far it has been impossible to 

 differentiate between them. 



*°Biitschli, O. — Protoplasm and Microscopic Foams (English transla- 

 tion), p. 117. 



