100 parts consist of | Water. | Carbon. Gum (pure gum-arabic) | 58.6 | 41.4 Sugar (pure crystallized) | 57.15 | 42.85 Starch | 56.00 | 44.00 Lignin | 50.00 | 50.00 These are so many mutually convertible products, of which gum may be looked upon as the basis; indeed gum is that organizable product which exists most universally in the proper juices of plants. "There are some instances in which sugar appears to be the first organic compound formed by the combination of the external elements, as when abundantly existing in the ascending sap of trees--the maple, for example. Starch may be considered as little else than gum divided into minute portions, each of which is enclosed in a membraneous cell (and containing some incidental particles, which, when starch is burnt, leave about .23 per cent. of residuum, consisting entirely of phosphates); and, in this state, it appears to answer very important ends in the vegetable economy. It is remarked by Decandolle, that, 'while gum itself may be considered the nutrient principle of vegetation, diffused freely through the structure of the plant, and constantly in action, starch is apparently the same substance, stored up in such a manner as not to be readily soluble in the circulating fluids,' thus forming a reservoir of nutritious matter, which is to be consumed, like the fat of animals (which it closely resembles in structure), in supporting the plant at particular periods[H]."