Browsing by Author "Caplan, Marc"

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    Effect of desiccation and storage on the seeds of two related species in the Amaryllidaceae from the western Cape Province
    (1993) Caplan, Marc; Farrant, Jill M
    This paper reports results on the first detailed physiological study undertaken on potentially recalcitrant seeds from the western Cape. Germination and dehydration behaviour of two related monocots Boophane flava Barker ex Snijman and Amaryllis belladonna L. (Amaryllidaceae) were studied to determine whether these seeds are indeed recalcitrant, and if so their degree of tolerance, and to gain an understanding of the reproductive strategies of these species through their seeds behaviour. Seeds were stored under mildly desiccating conditions, moisture content was determined at regular intervals and the ultrastructure of the hypocotyl apex tissue was examined. Both species are shed at high moisture content in a metabolically active state, and are able to tolerate considerable loss of this water (420-120% for B.flava) before water contents became lethal. Nevertheless, seeds were killed at high water contents a characteristic typical of recalcitrant seeds. A.belladonna seeds showed increased levels of subcellular organization during storage despite low viability scores. B.flava seeds showed hypocotyl extension and in a few instances roots and shoots were produced in storage, they began to lose viability after 8 weeks in storage at a moisture content below 120%. B.flava is a moderately recalcitrant seed species, with a slow germination rate. Although hypocotyl extension occurs in store, the onset of cell division and axis differentiation is delayed and occurred only . occasionally in store. This is interpreted as being ·a strategy to halt subcellular events which increase susceptibility to water loss. Seed maturity of B.flava is suggested to be polymorphic in response to an unreliable seasonal rainfall pattern.
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    Predicting the post-fire responses of two forest tree precursors after an autumn fire in mountain fynbos
    (1993) Caplan, Marc; Bond, William J
    This study investigated whether post-fire survival of two fynbos forest precursors Rapanea melanophloeos (L). Mez and Kiggelaria afri.cana L. were dependent on plant size or fire intensity. Two possible mechanisms of size dependent survival were investigated; 1) is fire survival the (ability to resprout) related to concentrations of root stored nonstructural carbohydrates (TNC) or 2) the protection afforded to epicormic buds through the thermal properties associated with bark thickness. Different sized saplings (4-40mm in basal diameter) of both species were planted before a controlled burn in autumn. TNC analysis was performed on a sub-sample of 5 plants from each size class prior to the burn. After the burn discriminant analysis were used to compare which pre- and post-fire variables are the most precise predictors of sprouting. Cambium death was found to be an accurate post fire predictor of mortality of both K. afri.cana and R.melanophloeos saplings. Stem height and basal diameter were good predictors of post-fire mortality of R.melanophloeos. Fire survival of K.afri.cana was independent of size, whereas R. melanophloeos showed a size dependent mortality, and trees with a basal diameter greater than 14mm having a 0. 78 probability of surviving the fire and a 0.67 probability of resprouting. Size dependent fire survival was not related to root TNC concentrations but to the survival of meristematic initials. These findings suggest that current fire management practices which favour cool burns, promote the expansion of forest patches into fynbos.