The Black Zones Formed by Wood-Desiroyincj Fuvgi 37 



position products which idtiiiiately infiltrate certain portions 

 of the wood, giving rise to blackish zoiies. 



(JJJEMICAL NATURE OF THE DECOMPOSITION 

 PRODUCTS. 



The indefinite and complex gronp of snbstances formed 

 by the partial decomposition of vegetable matter is generally 

 called " hnmns "' iuul so long as the word is used in a collec- 

 tive seaise as a convenient term it may be retained. From 

 its general properties we may infer that " humns " is a slowly 

 oxidizable colloid varying in color from brown to black. 

 Unfortunately wc cannot get much farther at the present 

 time. The partially decomposed material of woody plants 

 forms a particularly vague and indefinite group of substances 

 containing all the non-volatile products of fungal, enzymic, 

 and oxidative reactions on the plant residues. A detailed 

 study of this group being thus out of question we must first 

 ascertain what part it bears to the original woody substance 

 and then, when we know what to look for, try to discover 

 what particular constituents of the woody plant enter into 

 its formation. 



These decomposition products which subsequently infil- 

 trate certain portions of the wood are exceptionally resistant 

 to chemical reagents. IToald (1006) in discussing the de- 

 posits of it in Cottonwood due to Elfvingia. megaloma (Lev.) 

 Murrill, states that it is evidently insoluble in alcohol, ether, 

 caustic soda, caustic potash, hydrochloric acid, and only 

 slightly soluble in strong nitric acid. 



Stevens (1910, p. 367) states that wound gum may be 

 found lying free in the dead cytoplasm, surrounding starch 

 grains which have contributed to the formation of the gum- 

 like substance. He gives the properties of wound gum as fol- 

 lows : " Wound gum is not soluble in wann water, but may 

 be dissolved in hot nitric acid or in eau de Javelle after sev- 

 eral hours. It is not soluble in sulphuric acid, potassium 



