chapter X

) in composition. If this view should finally be established as a fact, this sub-group of supposed compound celluloses should be dropped from consideration as such.

PHYSIOLOGICAL USE OF CELLULOSES

There seems to be no question that the sole use of celluloses is to serve as structure-building materials. They are undoubtedly elaborated from the carbohydrates as the cell grows. In only rare cases, however, is there any evidence that they can be reconverted into carbohydrates to serve as food material. Certain bacteria can make use of cellulose as food, and secrete an enzyme, cytase, which aids in the hydrolysis of cellulose to sugars for this purpose. But this enzyme seems rarely, if at all, to be present in the tissues of higher plants. It has been reported that some cellulose is hydrolyzed during the malting of barley, indicating that this might have some food use for the growing seedling; but this observation has not been confirmed and later investigations seem to throw doubt upon its accuracy.

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.

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