. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. Fig. 423.—A thicket of pines that has succeeded a mixed growth of hard wood trees. killed off by fire or other cause, plants of an entirely different character will nearly always spring up to occupy its place. A forest of pine, for in- stance, is rarely fol- lowed by conifers, but by a growth of hardwood trees, and vice versa — nature thus giving an im- pressive example as to the effectiveness of a rotation of crops. Succession may be influenced by a va- riety of causes. T
. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. Fig. 423.—A thicket of pines that has succeeded a mixed growth of hard wood trees. killed off by fire or other cause, plants of an entirely different character will nearly always spring up to occupy its place. A forest of pine, for in- stance, is rarely fol- lowed by conifers, but by a growth of hardwood trees, and vice versa — nature thus giving an im- pressive example as to the effectiveness of a rotation of crops. Succession may be influenced by a va- riety of causes. Two of the most efficient are: (1) the exhaustion of the soil by the long-continued growth of one formation (60), thus causing a deficiency of mineral material suited- for the support of plants of that kind; (2) the migration of new species into the denuded territory where those which have different re- quirements as to min- eral nutrients from the former inhabitants will, other things being equal, have the best chance to succeed. 328. Invasion.—A rapid and widespread occupation of any terri- tory by a new species is called an invasion. No- table examples of inva- ders are those of the Russian thistle in the northwestern states of the Union, and the " bitterweed " (Helenium tenuifolium) that has almost driven out the hardy. Fig. 424. — A successful invasion — Japanese honeysuckle covering the banks of a ravins and climbing over shrubs and tree 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 Andrews, Eliza Frances, b. 1840; Lloyd, Francis Ernest, 1868-1947. ed. New York, Cincinnati [etc. ] American book company
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