Blade Tissue Organization of Foliage Leaves of Some Carolina Shrub-Bog Species as Compared with Their Appalachian Mountain Affinities

Abstract

1. Leaf blades of twenty-seven woody species of North Carolina have been studied. Leaves of fourteen species were collected from coastal shrub bogs; two, from coastal swamp forests; and eleven, from mesic forest habitats of the Appalachian mountain slopes. The selection of species was based upon a list prepared by B. W. Wells, showing how the shrubbog species have arisen: by geographical isolation from the Appalachians; by northern migration from the tropics; or by southern extension of boreal forms. Thus, the mountain species chosen are those that have Carolina coastal affinities. Conclusions are based upon comparative descriptive and statistical data from the group analyses as well as from data of the eight individual species pairs. 2. The leaves from both the shrub-bog and the mountain mesic forest collections are elliptical or modified elliptical, but the shrub-bog leaves are more perfectly elliptical. 3. The shrub-bog leaves are thick and, for the most part, coriaceous, evergreen, and heavily cuticularized, while those of the mesic forest are thinner, deciduous, and less cuticularized. 4. Greater volumes of palisade mesophyll account for most of the greater blade thickness of shrub-bog leaves as compared with the mesic mountain forms. The actual dermal volume for the two groups is about the same; both the palisade and the spongy mesophyll volumes are greater for the shrub-bog leaves, but the palisade volume is porportionally greater. 5. The shrub-bog leaf blades are smaller than are those of the mesic forest. Correlated with the smaller blade areas of the shrub-bog leaves are smaller surface areas of individual epidermal cells, smaller stomates, and higher stomatal frequencies. 6. Although the surface areas of epidermal cells are smaller for shrub-bog leaves, the cross-sectional area of the palisade cells for most of these leaves is larger; thus, the epidermal-palisade-cell ratio is smaller-that is, fewer palisade cells are contiguous to an epidermal cell. 7. In general, the shrub-bog leaves show less contrast between palisade and spongy mesophyll than do the mountain mesic forest leaves. For many of the bog leaves the vertically oriented palisade intergrades with a predominantly vertically oriented spongy mesophyll. 8. The radial walls of the epidermal cells are less sinuous in the shrub-bog leaves, especially in the leaves with thick cuticles. 9. The shrub-bog leaves have denser vein patterns than do the mesic leaves. 10. In the shrub-bog leaves the denser vein patterns are associated with greater palisade volumes and vertically oriented spongy mesophyll. 11. Five minor vein categories are described. Although all five patterns occur in leaves of both major groups studied, the dendriform, imbedded pattern is more frequent among shrub-bog leaves; veins carrying bundle sheath extensions and anastomosing around polygonal units of chlorenchyma occur more frequently among the mountain mesic leaves. 12. Those shrub-bog leaves which have anastomosing veins with bundle sheath extensions are the ones most heavily cuticularized. 13. The dendroid, imbedded vein patterns in the shrub-bog leaves are related to all-palisade mesophylls or to spongy mesophylls with predominantly vertically elongate and contiguous cells or parts of cells. 14. Leaves of both series have uniseriate dermal layers. 15. Crystal idioblasts and sclereids are associated with particular genera rather than with habitat. 16. Bundle sheath extensions are associated with anastomosing vein patterns rather than with dendriform vein patterns. 17. Hypotheses are proposed concerning the significance of certain blade characteristics of shrub-bog and mesic forest leaves, as to whether they are static, inherent characteristics or plastic responses to the immediate environment. The hypotheses are ones of induction based upon the occurrence of the blade characteristics within species groups or within individual species of paired affinities. Conclusions must be based upon experimental evidence.