Sugar

Sugar is formed in plant-cells as one of the earliest products of assimilation. It may possibly originate in the polymerisation of formic aldehyde, according to the equation:-

xCO₂ + xH₂O = xCH₂O + xO₂.

According to the recent researches of Messrs. Brown and Morris, the first sugar to be thus synthesised belongs to the saccharon or cane-sugar C₁₂H₂₂O₁₁) group. This acts apparently as a temporary reserve-material in the leaf until it passes a certain degree of concentration, when the more stable starch is formed, the first visible product. The cane-sugar passes into dextrose and levulose:-

C₁₂H₂₂O₁₁ + H₂O = C₆H₁₂O₆ + C₆H₁₂O₆.

Of these two, dextrose is apparently more quickly used up for respiration, and perhaps also for tissue-forming, so that most of the sugar that passes out of the leaf is levulose. The starch is translocated as maltose (C₁₂H₂₂O₁₁). Cane-sugar also occurs undoubtedly as a reserve-material in stems and roots, so that Sachs' summary of observations on the beet, "starch in the leaf, glucose in the petiole, cane-sugar in the root," might perhaps be modified into "cane-sugar, with starch as surplus, in the leaf, levulose in the petiole, and cane-sugar and starch in the axis."