. The ecological relations of roots . Fig. 33.—Surface view of a single root ofParonychia jamesii at a depth of 2 to 84 THE ECOLOGICAL RELATIONS OF ROOTS. to a point several feet on each side of the plant. A single plant thus lays holdof the surface soil to a depth of 18 inches or more within a radius of 4 or 5feet from its Apocynum androsaemifolium.—^Large areas, especially of the steeper gravelslides, are frequently covered by extensive communities in which this speciesis dominant, often forming famiUes (fig. 34). The vertical portions arisingfrom the horizontal rootstock a
. The ecological relations of roots . Fig. 33.—Surface view of a single root ofParonychia jamesii at a depth of 2 to 84 THE ECOLOGICAL RELATIONS OF ROOTS. to a point several feet on each side of the plant. A single plant thus lays holdof the surface soil to a depth of 18 inches or more within a radius of 4 or 5feet from its Apocynum androsaemifolium.—^Large areas, especially of the steeper gravelslides, are frequently covered by extensive communities in which this speciesis dominant, often forming famiUes (fig. 34). The vertical portions arisingfrom the horizontal rootstock are 2 to 5 mm. in diameter. From these|origi-. FiQ. 34.—Apocynum androscBmifolium, showing rhizomes and dense network of roots. nate groups of 2 to 5 erect stems. The rootstocks He at a depth varying from6 inches to 2 feet, but usually at about 8 to 16 inches. These run for distancesof 6 to 10 feet or more, giving rise at irregular intervals to erect portionswhich bear new plants. Sometimes these connected plants are only a fewinches apart, while at other times the interval between them may be 3 or 4 feet. The vertically ascending parts seldom have large branches, but are wellclothed with abimdant laterals 1 mm. or less in diameter. Thesefbranchesdivide and subdivide into many branch orders, forming brushlike mats which THE GRAVEL-SLIDE COMMUNITY. 85 run off in all directions to a distance of 6 or 8 inches or more. However, themost profound branching arises from the horizontal rootstocks. Like theformer, these are not large in diameter, but are branched so profusely, extend-ing vertically upward as well as downward and laterally
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Keywords: ., bookcentury1900, bookdecade1910, bookidecologicalre, bookyear1919
