Macrobotanical analysis: Charred parenchyma and endocarp Laboratory analysis

In document Agriculture in Tongan Prehistory: An Archaeobotanical Perspective (Page 154-156)

Macrobotanical remains were collected using three different methods during the excavation process. Any large charcoal fragments above 1cm in diameter observed during excavation of the test units were collected and placed in aluminium foil envelopes. These samples were labelled according to the site, test unit and spit from which they derived. Charcoal and seeds were also collected within both the light and heavy fractions during flotation. The light fraction floated during bucket flotation when water was added to the soil, and the heavy fraction remained in the bottom of the bucket to be wet-sieved. Some charcoal can become water-logged and therefore sinks during this process. This depends on the degree of charring within the fragments, and porosity of the material.

In the quarantine laboratory at the ANU, the heavy fraction was sieved through a 3mm mesh to create two size fractions, smaller and larger than 3mm. These fractions were then sorted into material and artefact types including shell, ceramics, land snails, seeds, and charcoal. These were bagged separately and labelled according to the site, test pit, spit and sample type (in situ, flot or wet-sieved). The flot (light fraction) was likewise sorted into material types such as charcoal, seeds, insect remains, pumice, small bone and landsnails. The charcoal from each of these sources, including in-situ, was then further sorted into parenchyma, wood charcoal and endocarp.

Charred endocarp

Where possible the endocarp was identified to genus or species level. This taxonomic identification was carried out first through the observation of surface morphology and features, and second through fracturing endocarp fragments down the radial section, and viewing the cell arrangement. Coconut (Cocos nucifera) has a distinctive surface texture on both the exterior and interior surfaces of the endocarp. This texture is created by a cell arrangement that creates a

137 ‘cross-hatched’ effect through long, thin parenchyma cells that stack horizontally and vertically alternately. Candlenut (Aleurites moluccana) is identifiable through distinctive surface morphology. The exterior surface of the endocarp has a bumpy and slightly warped texture similar to a walnut, and a high degree of curvature relative to fragment size.

Parenchyma

Parenchyma was identified to taxonomic level using the range of morphological features recorded within the comparative collection. Each fragment tentatively identified as parenchymatous was firstly described in terms of general and surface morphology (Hather 2000), and then fractured along the transverse and longitudinal planes to record cell arrangement and bundling features. The fractured parenchyma was placed into a small Petri dish and nestled in a bed of salt, and an Olympus Compound light microscope was used to view and image the fragments in reflected light. These fragments were confirmed as parenchyma based on morphology which differs from wood charcoal. These morphological traits include a more rounded surface due to the exposure and erosion of cells; surface features such as buds, detachment scars and spines; few visible rays and thus a more uneven fracture; consistent cell shapes that are usually rounded or angular; and the presence of distinctive vascular bundles or tissues.

Each fragment was identified as either stem or root-derived vegetative parenchyma, and then to species of origin where possible. The identification flowchart key was utilised to provide either a single identification or a list of possible identifications where no further breakdown of the taxa is possible due to morphological overlap, or other features of the archaeological parenchyma are not visible. These taxonomic identifications were then confirmed using images from both light microscopy and SEM. The images could also be utilised to eliminate or confirm taxa where a list of possible identifications is provided.

Classifications were then given based on the determination system outlined in Chapter 5 using identification criteria and associated levels of confidence compiled by Paz (2001) and by Oliveira (2008). This determination system has been used successfully by these researchers in the past to analyse macrobotanical plant remains from a range of archaeological contexts in the Asia-Pacific region (Barker et al. 2011; Barton and Paz 2007; Oliveira 2008; Paz 2001, 2005). The identification key is useful as a means of breaking down the morphology in the comparative collection. However, there was a reasonable likelihood that some samples would not match any of the specimens within the comparative collection due to both the condition of fragments and also the fact that the reference collection is not exhaustive. The reference collection also has a general focus on economic and non-economic plant taxa from Western Polynesia, and so would require the inclusion of additional specimens for use in other geographic locations.

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Chapter 8

Results

Presentation of results is divided into four main sections. The first section considers the quantification and identification of macrobotanical remains from all test units and sites. The various extraction techniques utilised in the field is also compared in terms of the effectiveness of the recovery of charred endocarp, wood charcoal and parenchyma. Each site will also be compared in terms of the quantities of identified material, the distribution of these in test units and the results of a case study presented for the identification of parenchyma at Talasiu. The second section focuses on the quantification and identification of microbotanical remains in the form of starch grains. Once again each site is compared in terms of starch preservation, the numbers of identified species and the distribution of starch within test units according to dated cultural deposits. The third section analyses a number of Western Pacific plant production systems using theoretical insights from Evolutionary and Human Ecology for assessing efficiency of yield and associated nutritional returns. These modern examples provide a useful range of models within which the past systems, represented by archaeobotanical remains, can be assessed and placed in the final section of this chapter.

Macrobotanical analysis

In document Agriculture in Tongan Prehistory: An Archaeobotanical Perspective (Page 154-156)