. Practical botany. Botany. STORAGE IX AXD LEAVES 77 69. Storage of food. Aerial stems contain plant food, often in great quantities. In the trunks of trees food is present in various forms, â as starch, sugar, oil, and proteins. Alany kinds of sapwood turn deep blue or black if tested with iodine for starch in the autumn. During the winter much of this starcli is often converted into sugar or oil. The presence of proteins in wood is so general that the cheaper grades of white paper, largely made of wood pulp, at once turn yellow on being mois- tened ^lâ ith nitric acid (protein t
. Practical botany. Botany. STORAGE IX AXD LEAVES 77 69. Storage of food. Aerial stems contain plant food, often in great quantities. In the trunks of trees food is present in various forms, â as starch, sugar, oil, and proteins. Alany kinds of sapwood turn deep blue or black if tested with iodine for starch in the autumn. During the winter much of this starcli is often converted into sugar or oil. The presence of proteins in wood is so general that the cheaper grades of white paper, largely made of wood pulp, at once turn yellow on being mois- tened ^lâ ith nitric acid (protein test). When thus tested, paper made wholly of cotton, or of linen rags, shows little change. The plant food stored in wood is most abundant in the younger portions (sapwood), and abo^-e all in the cambium laj'er. Underground stems often con- tain large quantities of stored food, and are thus useful in tiding over the period of the year when no food can be made, just as they have already (Sect. 66) been shown to be of serv- ice in storing water. There are many shade plants â such as trilliums, dogtooth violets (Fig. 66), wild ginger (Fig. 43), 3Iay apple (Fig. 59), and others â which leaf and blossom early in the spring and do a large part of the storing of food for the next season in their Fig. 63. The century plant of the preceding figure as it appeared nearly two months later The leaves have given up their stored food to the flowers and flower stalk and are now withered and valueless. Photograph by G. D. Fuller. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell, Otis William, 1869- joint author. Boston, New York [etc. ] Ginn and company
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