. Bulletin of the British Museum (Natural History) Botany. 74 N. K. B. ROBSON. Fig. 8 Stem lines in Hypericum and Ploiarium: (a) Hypericum revolutum; (b) H. perforatum; (c) H. bithynicum; (d) H. nilidum; (e) Ploiarium alternifolium. state in Hypericum; and it gives rise to 2-lined and then terete conditions, either by development (on the same woody shoot) or evolution (in some herbaceous species) (Fig. 8b, c). Occasionally six lines may be present in some internodes, in some species of sect. 20. Myriandra (Fig. 8d). Although these structures are usually no more than 'raised lines', they c
. Bulletin of the British Museum (Natural History) Botany. 74 N. K. B. ROBSON. Fig. 8 Stem lines in Hypericum and Ploiarium: (a) Hypericum revolutum; (b) H. perforatum; (c) H. bithynicum; (d) H. nilidum; (e) Ploiarium alternifolium. state in Hypericum; and it gives rise to 2-lined and then terete conditions, either by development (on the same woody shoot) or evolution (in some herbaceous species) (Fig. 8b, c). Occasionally six lines may be present in some internodes, in some species of sect. 20. Myriandra (Fig. 8d). Although these structures are usually no more than 'raised lines', they can be wide enough to be termed 'wings' ( in H. tetrapterum, sect. 9. Hypericum). The members of an opposite pair are always equally prominent; but there is almost always some difference between alternating pairs so that the lines decurrent from the leaf-bases (medians) are more prominent than those from between the leaves (laterals). Consequently, where there is only one pair of lines, these will almost always be medians. The exceptions to this rule occur in sect. 5. Androsaemum, where the sometimes 4-lined H. hircinum has laterals that are more prominent than the medians and the 2-lined H. androsaemum has laterals only. The association of stem-lines with leaves is clearer in Ploiarium alternifolium (Bonneti- oideae), in which the presence of stem-lines in the youngest parts is combined with spiral phyllotaxis. Although the lines are sometimes faint, three can be seen below each leaf, decurrent respectively from the midrib and each side of the petiole (Fig. 8e). It would. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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