JOST, L., trans. by GIBSON, R. J. H.--"Plant Physiology," 564 pages, 172 figs., Oxford, 1907. MARCHLEWSKI, L.--"Die Chemie des Chlorophylls," 187 pages, 5 figs., 7 plates, Berlin, 1909. PARKIN, JOHN.--"The Carbohydrates of the Foliage Leaf of the Snowdrop (_Galanthus nivalis L._) and their Bearing on the First Sugar of Photosynthesis," in _Biochemical Journal_, Vol. 6, pages 1 to 47, 1912. PFEFFER, W., trans. by EWART, A. J.--"Physiology of Plants." Vol. I, 632 pages, 70 figs., Oxford, 1900. CHAPTER IV CARBOHYDRATES These substances comprise an exceedingly important group of compounds, the members of which constitute the major proportion of the dry matter of plants. The name "carbohydrate" indicates the fact that these compounds contain only carbon, hydrogen, and oxygen, the last two elements usually being present in the same proportions as in water. As a rule, natural carbohydrates contain six, or some multiple of six, carbon atoms and the same number of oxygen atoms less one for each additional group of six carbons above the first one; e.g., C_{6}H_{12}O_{6}, C_{12}H_{22}O_{11}, C_{18}H_{32}O_{16}, etc. Carbohydrates are classed as open-chain compounds, that is, they may be regarded as derivatives of the aliphatic hydrocarbons. From the standpoint of the characteristic groups which they contain, they are aldehyde-alcohols. In common with many other polyatomic open-chain alcohols, they generally possess a characteristic sweet, or mildly sweetish, taste. In the case of the more complex and less soluble forms, this sweetish taste is scarcely noticeable and these compounds are commonly called the "starches," as contrasted with the more soluble and sweeter forms, known as "sugars." The characteristic ending _ose_ is added to the names of the members of this group. As systematic names, the Latin numeral indicating the number of carbon atoms in the molecule is combined with this ending; e.g., C_{5}H_{10}O_{5}, pentose, C_{6}H_{12}O_{6}, hexose, etc. In recent years, as a matter of scientific interest, many sugarlike substances which contain from two to nine carbon atoms combined with the proper number of hydrogen and oxygen atoms to be equivalent to the same number of molecules of water in each case, have been artificially prepared in the laboratory and designated as dioses, trioses, tetroses, pentoses, hexoses, heptoses, octoses, and nonoses, respectively. Substances corresponding in composition and properties with the artificial tetroses and one or two derivatives of heptoses are occasionally found in plant tissues, and a considerable number of pentoses and their condensation products are common constituents of plant gums, etc.; but the great majority of the natural carbohydrates are hexoses and their derivatives. GROUPS OF CARBOHYDRATES