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Wood anatomical characteristics for 21 taxa of Cassiope are reported. Qualitative features differ somewhat from the general pattern of the Ericaceae. However, considerable deviation is found in the quantitative aspects of the wood features. The stems are very slender with narrow growth rings evident in all but one species. Vessel elements are very small and usually have scalariform perforation plates with several bars. Vessels are extremely abundant in transection. Vascular rays are mostly uniseriate with a few biseriates and all are composed exclusively of erect cells. The imperforate elements are tracheids which are the only conductive elements in the late wood. Calluna-type pith is found in most of the taxa while homogeneous pith is found in two species. The recognition of these in the separate genus Harrimanella is supported. Cassiope plants are often found in moist, protected microenvironments in arctic and alpine areas of extreme cold and desiccating winds. Short growing seasons and low mean temperatures probably contribute in large part to the dwarf stature of the plants, which in turn accommodates the reduced vascular system. The tracheids provide a safe conductive system in the late wood which is less susceptible to loss of function due to air embolisms. The vessel elements with scalariform perforation plates accommodate the presumably slow conductive rates in the earlier part of the growing season. The vessel elements of Cassiope are considerably smaller than most others known to have scalariform perforation plates. The values for vulnerability, an indicator of the degree of vessel redundancy and hence safety, are much lower than any yet calculated for any group. The same is true for figures for mesomorphy, which introduces vessel element length as an independent measure of degree of xeromorphy.

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© 1986 Gary D. Wallace

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