Abstract
THE theory which regards the alternate arrangement of leaves as the normal mode receives some support from the arrangement of the inflorescence of opposite leaved plants. In Lysimachia nemorum the leaves are opposite, inflorescence indefinite, solitary, and axillary, but it will be observed that the flowers springing from the axils of opposite leaves are never both equally developed at the same time, one will be fully expanded while the other is yet in bud, or one will be found in seed and the other in. flower; it will be further observed that the oldest or most fully developed flower appears alternately on opposite sides of the stem; if all the leaves on this plant were separated by internodes, the arrangement would be tetrastichous, but owing to the suppression of the internodes between the first and second and the third and fourth leaves, the arrangement becomes opposite. The oldest of the two opposite flowers of each pair of leaves will be found to spring from the axil of the first, third, and fifth leaf, and plants with this alternate disposition of flowers may sometimes be met with; but usually a flower originates in the axil of each leaf, and then the youngest or latest flowers spring from the second and fourth leaves of the verticil; these latter may be looked upon as originating from arrested branches. This view is supported by the fact that plants may be sometimes found which, in place of producing the late flowers in the axils of the third and fourth leaves, produce branches from these points instead. In Caryophyllaceæ the opposite sides of the cymose inflorescence never exhibit an equal amount of development at the same time, proving that one of the sides is older than the other, although, owing to non-development of an internode, it is at the same level. A similar arrangement occurs in Labiate plants, but owing to the crowded inflorescence, it is not so evident, but it is very marked where branches spring from opposite leaves; one is generally two or three times as long as the other, and by tracing the arrangement of these long branches along the stem, the normal alternate arrangement may be determined. In Scrophulariaceæ, where both opposite and alternate leaves are met with, all the above-mentioned modifications may be seen. Veronica chamædrys has opposite leaves, and when the axillary racemes are opposite, one is invariably more developed than the other; this can be best seen by examining the inflorescence in the young state, as the dissimilarity in size disappears in the pairs of old racemes owing to the younger of the two continuing to grow until it has acquired the size of the other; sometimes this plant may be met with bearing in the axil of one of its opposite leaves a branch, and a raceme of flowers in the other, and in such instances the branches and flowers are produced on alternate sides; in V. officinalis this is the usual arrangement. The suppression of the alternate nodes of an alternate-leaved plant with axillary inflorescence would produce the arrangement seen in Lysimachia, inasmuch as it would bring together flowers of different ages and in different stages of expansion; but in this instance all the flowers would belong to the same generation or be the product of the same stem, whereas in Lysimachia the earliest developed of each pair of opposite flowers alone belong to the stem, while the later flower of each pair belong to another generation, and spring from a branch originating in the axil of the leaf opposite (owing to non-development of an internode) to the early flower; the branch, however, is generally arrested, and the flower alone appears, although sometimes the branch is more or less developed.
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MASSE, G. Phyllotaxis. Nature 16, 208 (1877). https://doi.org/10.1038/016208b0
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DOI: https://doi.org/10.1038/016208b0
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