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DISCUSSION

Baltic amber has been well known for its inclusions for centuries, and speculation on its origins as a tree resin dates certainly as far back as Pliny the Elder in 49 AD and perhaps earlier (Healy 2004, Clark 2010). Many have suggested that the origin of the resin may have been a variety of pine tree (Healy 2004, Clark 2010) and some have suggested the name Pinites succinifer (Göppert 1846). Despite the similarity of the resin to the conifer families Araucariaceae and Pinaceae, it may be that the tree that produced the resin was more closely related to the Sciadopityaceae which is now represented by a single species Sciadopitys verticillata (Japanese Umbrella-pine) (Wolfe et al. 2009).

 

This study was unable to obtain the depth penetration, nor the differential fluorescence between the insect and the amber resin, necessary to obtain insect images similar in quality to those obtained by Böker & Brocksch (2002). Both the insects and the amber fluoresce in the ultra-violet part of the spectrum making it difficult to distinguish between them.

 

Trichomes are known to contain (blue-green) autofluorescent flavanoids. The samples of amber have strong autofluorescence in the UV range which enables discrimination of amber from the embedded trichome.  Our initial observations of a strong autofluorescence in the far red spectrum suggest the presence of an alternative compound or a modified form of flavonoid present within amber-included trichomes.  Alternatively, the trichomes may have been transformed and/or chemically altered over time.  Whilst this certainly warrants further study, the main aim of this project was to examine the structure of the trichomes and assess the usefulness of CLSM. 

 

The Mexican trichomes examined in this study differ from the trichomes from Baltic amber and may belong to the Family Euphorbiaceae.

 

The individual Baltic trichome that was chosen for the study has a stellate form with seventeen radii (figures 1, 2; animation 1). Overlapping radii give the appearance of bifurcation, but when viewed in 3D, it is evident that they are separate radii. The trichome appears to have two stellate clusters superimposed on each other (geminate). One of the radii is longer than the others perhaps representing a stalk. The trichome here is consistent with the structure of trichomes of the Fagaceae, or oak family (Hong-Ping et al. 1990, Nixon 2002, González-Villarreal 2003a, 2003b).

 

CLSM may be further developed to help with producing 3D images of inclusions in amber. Although the technique seems to be limited by the size of the inclusions and the depth at which the inclusion appears, Böker & Brocksch (2002) have shown that it is possible to produce high definition 3D images of larger insect inclusions. The equipment at the University of Glasgow is not optimised for such analyses, but has been useful in producing 3D images of very small trichome inclusions. Further refinement of this technique and equipment may allow useful systematic study of inclusions in amber by providing very high resolution 3D imagery of the anatomy of inclusions.

 

Scanning of amber using computed tomography and phase contrast X-ray synchrotron microradiography has provided the opportunity for 3D analysis of larger fossil inclusions (Polcyn et al. 2002, Lak et al. 2008, 2009). This technique provides very high resolution 3D images of the fossil contents of the amber and has been particularly useful in examining opaque amber (Lak et al. 2008). The long term effects of exposure to a high energy monochromatic beam on amber are unknown, but the benefit of being able to visualise the contents of opaque amber is great.

 

CLSM has limited usefulness in the analysis of amber inclusions due to the lack of penetration and the reliance on the differential fluorescence between the inclusions and the amber. Nevertheless, CLSM has potential value in recognising different fluorescing properties perhaps providing an indication of different compositional or structural architecture.

 

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