. The Indiana weed book. Weeds. 32 THE INDIANA WEED Fig. 7. Fibrous roots of red clover showing the nitrogen storing nodules. (After Piper.) nodules caused by bacteria. (Fig. 7.) These bacteria have the power to fix the free nitro- gen of the air and develop ni- trogen salts. The clover plant uses part of these nitrogen salts as food and leaves some of them in the ground. Weeds of the pea family are thus to some degree beneficial in that they help enrich the soil. The roots of most biennial weeds, aswell as those of some perennials, are often thick or fleshy, being composed largely of
. The Indiana weed book. Weeds. 32 THE INDIANA WEED Fig. 7. Fibrous roots of red clover showing the nitrogen storing nodules. (After Piper.) nodules caused by bacteria. (Fig. 7.) These bacteria have the power to fix the free nitro- gen of the air and develop ni- trogen salts. The clover plant uses part of these nitrogen salts as food and leaves some of them in the ground. Weeds of the pea family are thus to some degree beneficial in that they help enrich the soil. The roots of most biennial weeds, aswell as those of some perennials, are often thick or fleshy, being composed largely of starch which has been stored to be used in giving the flower stems of the second or succeed- ing year nourishment for a quick growth in spring. Such weeds often have one large central tap-root extending straight downward, with a few smaller roots branching from its sides. The roots of a weed extend downward or outward in search of a suf- ficient supply of moisture; if this be lacking the weed, like all other plants, ceases growth, shrivels and in time dies. The stems op weeds.—The stem is the main axis of the plant and is supposed to bear the roots below ground and the leaves and flowers above. Most stems of weeds are more or less branched, some of them very much so; if not at all branched they are called simple. If the stem dies down to the ground each year the plant is called an herb, or if it twines, an herbaceous vine. Almost all weeds are herbs. Stems with a woody texture which survive the winter above ground are woody vines, shrubs or trees. One shrub and two woody vines are included in the list of Indiana weeds, viz., the blackberry, poison ivy and trumpet-creeper, while the common elder might with propriety also have been included. In structure stems of weeds and other flowering plants are di- vided into two great classes. In one class, called endogens, or in- side growers, the woody or vascular tissue is usually scattered in bundles through the stem, and there is no
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectweeds, bookyear1912
