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ABSTRACT. The paired comparison (PC) (JEL 426)

Roots of representative epiphytic orchids were examined for anatomical detail, desiccation resistance and evidence of CAM activity. Those "shootless" taxa examined (Campylocentrum pachyrrhizum (Reichenb. f.) Rolfe, Harrisella porrecta Reichenb. f.) Fawc. & Rendle, and Polyradicion lindenii (Lindl.) Cogn. ex Urban) and a semi-shootless type (Kingidium taeniale (Lindl.) P. F. Hunt) bear thinner or eroded velamina and greater volumes of cortical intercellular space than do those of the leafy forms tested (Campylocentrum sellowii (Reichenb. f.) Rolfe, Encyclia tampensis (Lindl.) Small, Epidendrum radicans Pavon ex Lindl., Phalaenopsis amabilis (L.) Blume, Rangaeris amaniensis (Krzl.) Summerhayes and Vanda parishii (Reichenb. f.)). Shootless species also bear a more elaborate aeration apparatus at the velamen-cortex interface. Structurally distinct cortical cells located in this region may regulate gas exchange across the exodermis. Velamen thickness varies greatly among the ten species, as does the development of outer tangential walls of U cells in the underlying exodermis. Desiccation resistance under laboratory conditions was more closely related to root surface-to-volume ratio (S/V) than to any other measured anatomical parameter, including velamen development. Modes of carbon gain and the possible pathway for movement of fungus-borne carbon into an orchid's pool of assimilates are described, as is the possible significance of these processes to survival in forest canopy habitats.

Traditional travel cost analysis has either ignored multiple destination trips or arbitrarily allocated trip costs across visited sites. In this paper, combinations of multiple destinations are treated as unique sites and incorporated into a demand system. Empirical demand functions for multiple destination trips that include Bryce National Park are estimated. Consumer surplus calculations for single destination and multiple destination trips are compared.