WATER RELATIONS OF POCOSIN OR BOG SHRUBS

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Abstract
Transpiration studies involving the pocosin or shrub bog spp., Clethra alnijolia, Gordonia lasianthus, Ilex glabra, and Myrica cerifera, were made. A study of the habitat, with special attention being given to those factors which are directly or indirectly involved in the water relations of these plants, was carried out simultaneously. There was no evidence that the coriaceous leaf structure of these species is an adaptation enabling the plants to survive physiological or physical drought by virtue of low transpiration rates. The phytometer studies proved that the pocosin spp., growing in fairly well aerated soil- with moisture content near the field capacity, have transpiration rates comparable to those of such mesophytes as Quercus alba, Q. borealis var. maxima, and Liriodendron tulipifera. The absorption rates of these spp. were reduced by poor aeration. Observations extending over 3 yrs. indicate that generally during periods when atmospheric factors favor high transpiration rates the shallow root systems are seldom submerged for more than a few days at a time. The problem of aeration of the pocosin habitat, therefore, seems to be of less importance than has commonly been supposed. There seems to be no basis for considering the pocosin a "physiologically dry" habitat and the coriaceous leaf structures of these spp. cannot be explained in terms of water relations.