Elementary botany . relation of dis-tance of leaves on the stem to length of the upper and lower - ^ *v\>^?•• ?,!. ^.*:V . -. .^ S\ . ** .. > £2feg|s§i H * . • Fig. showing radiate arrangement of leaves and the petiole of the leaf func-tions as stem in lifting leaf to the light. leaves; the number of vertical rows on the stem compared tothe width of the leaves; and the relation of these facts to theproblem of light supply. Related to the spiral pattern is that oferect stems with opposite leaves. Here each pair is set at rightangles to the direction of the pair above or b
Elementary botany . relation of dis-tance of leaves on the stem to length of the upper and lower - ^ *v\>^?•• ?,!. ^.*:V . -. .^ S\ . ** .. > £2feg|s§i H * . • Fig. showing radiate arrangement of leaves and the petiole of the leaf func-tions as stem in lifting leaf to the light. leaves; the number of vertical rows on the stem compared tothe width of the leaves; and the relation of these facts to theproblem of light supply. Related to the spiral pattern is that oferect stems with opposite leaves. Here each pair is set at rightangles to the direction of the pair above or below. 781. Radiate pattern.—This pattern is present in many grassesand related plants with narrow leaves and short stems. Theleaves are often very crowded at the base, but by radiating inall directions from the horizontal to the vertical, abundant ex- nrmTTi FOLIAGE LEAVES. 409 posure to light is gained with little shading. The dragon treescrew-pine, and plants grown in greenhouses also illustrate this. Fig. pine (Pandanus) showing prop roots and radiate pattern of leaves. type. It is also shown in cycads, palms, and many ferns, althoughthese have divided leaves. 782. Compass plants.—These plants with vertical leaf arrange-ment, and exposure of both surfaces to the lateral rays of lighthave been mentioned in other sections (Lactuca scariola). 783. Open patterns.—Open patterns are presented by dividedor branched leaves. Where the leaves are very finely dis-sected, they may be clustered in great profusion and yet admitsufficient light for some depth below. Where the leaflets arebroader, the leaves are likely to be fewer in number and soarranged as to admit light to a great depth so that successiveleaves below on the same or adjacent stems may not be too muchshaded. On such plants, often the leaves lying next the groundare entire or less divided. CHAPTER XLI. THE ROOT I. Function of Roots. 784. The most obvious function of the roots of ordinary plantsare tw
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