Wednesday, 21 January 2015

Microfossil of the Month: Plant Stomata

For 2015 I have decided to replace my Micrograph of the Month feature with Microfossil of the Month. I will likely return to the thin section micrographs at some point, but as I am going to be working on phytolith and ash samples for most of this year, I figured it would make sense to feature some of these on the blog! Who knows how long I will be able to keep it up - from past experience of the sites I am working on, I may be limited in the range of examples that I will find! As a refresher (and for those of you new to the blog), microfossils are any fossil remains that are too small to see easily with the naked eye, but can be identified under the microscope. I work on plant microfossils, specifically silica phytoliths, which are 3D 'impressions' of plant cells and tissue. When the plant is alive, it takes up silica from the ground, which is then deposited inside and between the cells, forming 3D replicas of the cells that preserve when the organic part of the plant decays. The formation of phytoliths is complex and not well understood, but is controlled by a wide range of factors, with water availability being an important one. The more water that is taken up, the more silica that is taken up, and so plants which have a high water availability tend to produce lots of phytoliths.

The example here shows a sections of plant tissue (i.e. lots of single cells joined together). The rounded shapes that you can see are a distinctive type of plant structure, the plant stoma (plural stomata), a pore/opening in the skin which is formed from two guard cells. These openings are where the plant takes up carbon dioxide and releases oxygen in respiration, and also where water vapour leaves the plant during transpiration. This fragment of reed leaf/stem comes from an ashy midden deposit at the early Neolithic site of Boncuklu in Turkey, and are a blackish colour from burning.

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