Summary Epidermal cells of leaves are diverse: tabular pavement cells, trichomes, and stomatal complexes. Pavement cells from the monocot Zea mays (maize) and the eudicot Arabidopsis thaliana (Arabidopsis) have highly undulate anticlinal walls. The molecular basis for generating these undulating margins has been extensively investigated in these species. This has led to two assumptions: first, that particular plant lineages are characterized by particular pavement cell shapes; and second, that undulatory cell shapes are common enough to be model shapes. To test these assumptions, we quantified pavement cell shape in epidermides from the leaves of 278 vascular plant taxa. We found that monocot pavement cells tended to have weakly undulating margins, fern cells had strongly undulating margins, and eudicot cells showed no particular undulation degree. Cells with highly undulating margins, like those of Arabidopsis and maize, were in the minority. We also found a trend towards more undulating cell margins on abaxial leaf surfaces; and that highly elongated leaves in ferns, monocots and gymnosperms tended to have highly elongated cells. Our results reveal the diversity of pavement cell shapes, and lays the quantitative groundwork for testing hypotheses about pavement cell form and function within a phylogenetic context.

The epidermal cells of leaves lend themselves readily to observation and display 1 many shapes and types: tabular pavement cells, complex trichomes, and stomatal 2 complexes 1 . Pavement cells from Zea mays (maize) and Arabidopsis thaliana (arabidopsis) 3both have highly undulate anticlinal walls and are held as representative of monocots and 4 eudicots, respectively. In these two model species, we have a nuanced understanding of the 5 molecular mechanisms that generate undulating pavement cell shape 2-9 . This model-system 6 dominance has led to two common assumptions: first, that particular plant lineages are 7 characterized by particular pavement cell shapes; and second, that undulatory pavement cell 8shapes are common enough to be model shapes. To test these assumptions, we quantified 9 pavement cell shape in the leaves of 278 vascular plant taxa and assessed cell shape metrics 10 across large taxonomic groups. We settled on two metrics that described cell shape diversity 11well in this dataset: aspect ratio (degree of cell elongation) and solidity (a proxy for margin 12 undulation). We found that pavement cells in the monocots tended to have weakly undulating 13 margins, pavement cells in ferns had strongly undulating margins, and pavement cells in the 14 eudicots showed no particular degree of undulation. Indeed, we found that cells with strongly 15undulating margins, like those of arabidopsis and maize, were in the minority in seed plants. 16At the organ level, we found a trend towards cells with more undulating margins on the abaxial 17 leaf surface vs. the adaxial surface. We also detected a correlation between cell and leaf 18 aspect ratio: highly elongated leaves tended to have highly elongated cells (low aspect ratio), 19but not in the eudicots. This indicates that while plant anatomy and plant morphology can be 20 connected, superficially similar leaves can develop through very different underlying growth 21 dynamics (cell expansion and division patterns). This work reveals the striking diversity of 22 pavement cell shapes across vascular plants, and lays the quantitative groundwork for testing 23 hypotheses about pavement cell form and function. 24

Understanding the composition of the paints used on works of art is crucial in attributing them to the artist or workshop that created them, as well as to devising strategies for their preservation and restoration. Much current research is focussed on the development of non-invasive spectroscopic methods, enabling in situ paint analysis without the need for sampling. However, whilst a lot of work has been carried out on looking at the composition of artists' materials qualitatively, little has been performed to analyse them quantitatively. In this work, we investigate the use of Fourier transform Raman spectroscopy, in isolation and in conjunction with complementary fibre optic reflectance spectroscopy, to look at the spectral changes that occur with varying the paint/binder ratio in model historic lead-based paints. When used in conjunction with multivariate analysis, we demonstrate that it can be possible to obtain a semi-quantitative estimation of the composition of a paint film from its Fourier transform Raman spectrum, given a set of suitable reference spectra recorded from paints produced within the workable mixture range. This represents a tentative first step towards a semi-automated and quantitative method for analysing cultural heritage objects, which may help boost our understanding of their history, and enable conservators to make more informed decisions so as to ensure their preservation.