. The elements of botany for beginners and for schools. Botany. SECTION 7.] THEIR ARRANGEMENT. 71 be made out by direct inspection. They may be indirectly ascertained, how- ever, by studying the secondary spirals, as they are called, which usually become conspicuous, at least two series of iheiii, one turning to the right and one to the left, as shown in rig. 191. Eor au account of the way in which the character of the phyllotaxy may be deduced from the secondary spirals, sec Structural Botany, Chapter IV. 193. Phyllotaxy of Opposite and wliorled Leaves, This is simple and comparatively unifor
. The elements of botany for beginners and for schools. Botany. SECTION 7.] THEIR ARRANGEMENT. 71 be made out by direct inspection. They may be indirectly ascertained, how- ever, by studying the secondary spirals, as they are called, which usually become conspicuous, at least two series of iheiii, one turning to the right and one to the left, as shown in rig. 191. Eor au account of the way in which the character of the phyllotaxy may be deduced from the secondary spirals, sec Structural Botany, Chapter IV. 193. Phyllotaxy of Opposite and wliorled Leaves, This is simple and comparatively uniform. The leaves of each pair or whorl are placed over the intervals between those of the preceding, and therefore under the intervals of the pair or whorl next above. The Avhorls or pairs alternate or cross each other, usually at right angles, that is, Ihey decussate. Opposite leaves, that is, whorls of two leaves only, are far com- moner than whorls of three or four or more members. This arrangement in successive decussating pairs gives au advantageous distribution on the stem in four verti- cal ranks. Whorls of three give six vertical ranks, and so on. Note that in descriptive botany leaves in â whorls of two are simply called opposite leaves; and that the term verticillate or whorled, is employed only i'or cases of more than two, unless the latter number is specified. 194. Vernation or Praefoliation, the disposition of the leaf-blades in the bud, comprises two things ; 1st, the way in which each separate leaf is folded, coiled, or packed up in the bud; and 2d, the arrangement of the leaves in the bud with respect to one another. The latter of course depends very much upon the phyllotaxy, i. e. the position and order of the leaves upon the stem. The same terms are used for it as for the arrangement of the leaves of the flower in the flower-bud. See, therefore, " Estivation, or ; 195. As to each leaf separately, it is sometimes straight and open in verna
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