Abstract
AT a meeting of the Biological Society of Washington (United States), held on December 15, 1888, Mr. Lester F. Ward read a paper on “Fortuitous Variation, as illustrated by the genus Eupatorium.” He exhibited a series of specimens of that genus, mostly from the vicinity of Washington, and growing in great part in the same kind of soil and under the same general conditions. To simplify the question, the differences in the flowers, heads, and reproductive parts in general, which are less marked in this than in almost any other genus, were ignored, and attention was exclusively directed to the leaves. These, when closely compared, are seen to differ considerably in the different species, the forms ranging from the filiform dissected leaves of E. fæniculaceum to the broad ovate leaves of E. ageratoides. But between these extremes there are represented in the Washington flora numerous much more similar forms, which present to the observer a strongly marked family resemblance; from those with more elongate leaves, such as E. altissimum, E. album, and E. teucrifolium, through the increasingly broader more ovate forms, E. perfoliatum, E. sessilifolium, and E. rotundifolium ovatum (E. pubescens, Muhl.), with an intermediate undescribed form, which Dr. Gray regarded as a hybrid, connecting the last two to the typical E. rotundifolium, with its roundish, crenate, but still sessile leaves; and from this last form, with several similar Mexican species, on in the direction of acquiring a petiole, through several exotic forms, to E. cælestinum, E. aromaticum, and E. ageratoides, in an almost unbroken chain of modifications without any apparent advantage to the plants. Almost any other genus might have served the purpose of the paper, but this one seemed to possess the merit of simplicity.
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Fortuitous Variation. Nature 40, 310 (1889). https://doi.org/10.1038/040310a0
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DOI: https://doi.org/10.1038/040310a0