1902.] natural scfexces of philadelphia. 481 



Contexts of Plugged Tracheids and Filled Medullary 

 Ray Celi>;. 



The Unverdorben-Fraucliimoiit reaction with copper acetate was 

 used as a special reagent to determine the presence or absence of 

 resins and terpenes.'^- It was thought that the material plugging the 

 tracheids and filling some of the medullary ray cells might he of a 

 resinous nature. The reaction is indecisive as to the material in 

 the tracheids. An emerald-green color is produced by the copper 

 acetate in the area of wood most affected by the fungus and where 

 the active formation of the wood and bast took place. This green 

 color is confined to the newly formed sap-wood and to the immediate 

 neighborhood of the most active mycelial growth. The appearance 

 of the emerald-green color indicates the presence of resin, and, in 

 fact, in thin longitudinal sections of the wood of the stem at the 

 .swelling there is found a granular matter which stains a malachite- 

 green. This material, which reacts to the copper acetate, occurs as 

 a peripheral layer about the brownish matrix in the center of the 

 filled medullary ray cells and the plugged tracheids, and this is 

 most pronounced where the influence of the fungous parasite seems 

 to be most marked. In some cases the green color indicates that 

 whole medullary ray cells contain a resinous material. The con- 

 tents of the resin canal cells of the phloem and of the cortex react 

 to the copper acetale, and the dried resin which occurs on the surface 

 of and in the fissures of the bark becomes of a striking malachite- 

 green Qolor. These latter reactions confirm the Unverdorbeu- 

 Franchimonl test. The green color imparted to the wood is con- 

 fined to patches and is not generally distributed. The brown 

 material in general of the plugged tracheids and medullary ray 

 cells is not influenced by the copper acetate. That this reaction 

 seems to indicate the presence of resin in the most diseased areas 

 and another fundamentally different substance is indicated by the 

 fact that adjoining cells will have their contents colored emerald- 

 green, while others will remain uniformly uncolored. In a trans- 

 verse section of the area of wood stained green, the contents of 

 the plugged tracheids (figs. 16, 17) still retain their brownish- 

 yellow color. Notwithstanding these facts, one point .-^eems to be 

 definitely settled, viz., that the presence of the mycelium in the 



"ZiMMERMANN-HuMPHREY, Botaiiical Microtechnique, pp. 90, 91. 

 31 



