Botanists who study the tissues of Living plants, or those palæobotanists who deal with actual petrifactions, have scarcely any idea of the difficulties that meet the worker on carbonised plantremains, especially when the material is so limited that the research cannot be repeated in the event of damage to a single preparation. Moreover, the research can be conducted only on those portions of the tissue that are cutinised, since all the rest have been carbonised or destroyed in the course of fossilisation, and no longer appear after the preparations have been bleached. The student of Mesozoic plants is in the further unhappy position that, with a few notable exceptions, he rarely finds portions of the plant that show any structure; he in particular must direct his attention to the cutinised membranes, and above all to the cuticle of the leaves and stems and, in the case of Pteridophyta, to the spores.