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THE ORIENTATION OF PRIMARY TERRESTRIAL ROOTS WITH PARTICULAR REFERENCE TO THE MEDIUM IN WHICH THEY ARE GROWN
Author(s) -
Holman Richard M.
Publication year - 1916
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1916.tb05415.x
Subject(s) - citation , orientation (vector space) , library science , computer science , mathematics , geometry
The orientation of plant organs relative to external agencies has long been a subject of interest, not alone to botanists but to those without botanical knowledge as well. The fact that the trunks of the trees on a steep mountain slope orient themselves without reference to substratum and grow parallel to the direction in which the attraction of gravity operates illustrates no less forcibly than does the familiar bending of the stems of house plants toward the window from which they receive light the importance of external factors in directing the plant's growth. Similar phenomena are not uncommon among animals, although, aside from our own dependence upon gravity for the orientation of our bodies, there are about us fewer examples which are obvious to the untrained observer, of the directive effect of gravity, light and other external factors upon animals. There are, however, among those animals which, like most plants, remain attached during all or a part of their existence, many cases in which the orientation of the organism is dependent upon gravity, one-sided illumination or other external agencies acting in a definite direction. Unattached and motile animals can, in many cases, be shown to have the direction of their movements definitely determined by these and other external factors. Plants offer, however, more favorable material for the study of the directive influence of these agencies which are not diffuse in their application to the organism but which operate or can be caused to operate in a constant direction. The subterranean parts of the plant as well as the structures above ground are under the influence of various agencies which affect the direction of their growth. Chief among these is gravity, and the terrestrial root furnishes a particularly favorable object for the study of the directive influence of gravity. More investigation has probably been devoted to the study of the geotropism of roots than to any other subject related to the