Bacteria of decay also act upon cellulose materials, converting them chiefly into gaseous products; but this seems to be a provision of nature for the destruction of the cell-wall material of dead plants, rather than an arrangement for the constructive use of it as food for the bacterium. When fibrous plant residues decay in the soil, the cellulose compounds are first converted into a series of complex organic acids, known as "humins," which undoubtedly have a significant effect upon the chemical and physical properties of the soil, but these have little interest or significance in a study of the chemistry of plant growth. REFERENCES ABDERHALDEN, E.--"Biochemisches Handlexikon, Band 2, Gummisubstanzen, Hemicellulosen, Pflanzenschleimen ..." 729 pages, Berlin, 1911; and "Band 8--1 Ergänzungsband (same title as Band 2)--," 507 pages, Berlin, 1914. SCHWALBE, C. G.--"Die Chemie der Cellulose," 665 pages, Berlin, 1911. CHAPTER VI GLUCOSIDES Strictly speaking, the term _glucoside_ should be applied only to such compounds as contain glucose as the characteristic basic group. But in common usage, it refers to any compound which, when hydrolyzed, yields a sugar as one of the products of the hydrolysis. In all the natural glucosides which occur in plant tissues, the other organic constituent, which is represented by the R in the formula for glucosides (R·C_{6}H_{11}O_{5}, or R·(CHOH)_{5}CHO) is some aromatic group, or closed-ring benzene derivative.[3] The different organic constituents of glucosides are of a great variety of types, such as phenols, alcohols, aldehydes, acids, oxyflavone derivatives, mustard oils, etc. It is noteworthy, however, that no nitrogenous groups of the protein type have been found combined with sugars in glucosides. Some glucosides contain more than one saccharide group, possibly as di- or trisaccharides. Under proper conditions of hydrolysis, one or more of the saccharide groups can be removed from such compounds, resulting in glucosides of simpler structure. Most of the common glucosides are derived from _d_-glucose. Some are known, however, which are derivatives of galactose or rhamnose; while in some cases the exact nature of the sugar which is present has not yet been determined. FOOTNOTES: [3] HC // \ HC CH The structural formula for benzene, C_{6}H_{6}, | ║ is one which it is HC CH \\ / CH difficult and inconvenient to reproduce in type. On that account, it is