How little advance had been made towards the true understanding of the varieties of forms of tissue in the higher plants before 1850 is shown, for instance, by Schleiden’s account of tissues on page 232 of his ‘Grundzüge’ of 1845, where parenchyma, intercellular substance, vessels, vascular bundles, bast-tissue, bast-cells in Apocyneae and Asclepiadeae, laticiferous vessels, felted tissue, epidermal tissue, are discussed in this succession in co-ordinated sections of the text. It is obvious that no well-ordered view of the whole cellular structure of a plant of the higher order could be obtained in this way. Further on in the same work, where Schleiden attempts a classification of vascular bundles, which he distinguishes into closed and open, and assigns the latter to Dicotyledons, we find the cambium-layer named as the outer boundary of these open vascular bundles; the bast which lies outside the cambium was therefore not considered to be a part of the open vascular bundles, and this necessarily excluded any profitable comparison of the circumstances in Monocotyledons and Dicotyledons. The case is still worse in many respects in Schacht’s work already mentioned, ‘Die Pflanzenzelle’ of 1852, where under the heading ‘Kinds of vegetable cells’ the histology is discussed in the following co-ordinated sections; the swarm-filaments of Cryptogams, the spores of the same, pollen-grains, cells and tissue of Fungi and Lichens, cells and tissue of Algae, parenchyma and its cells, vessels of the plant, wood and its cells, bast-cells, stomata, appendicular organs of the epidermis, cork; then follows a paragraph on the thickening-ring, and then to the no small astonishment of the reader comes an account of the vascular bundles, after the vessels, the wood, and the bast-cells have been already dismissed. That such a mode of presenting the subject is due to the little insight possessed by the writer into the structure of the plant as a whole is apparent from simply reading the book, and a similar confusion of ideas is found in his text-book of 1856. We find a much better classification of tissues in 1855 in Unger’s ‘Anatomie und Physiologie der Pflanzen’; an account of cells is followed by a description of cell-complexes, as one of the chief divisions of the book, and herein of cell-families, cell-tissues, and cell-fusions. Another chief section is occupied with cell-groups, and here epidermal formations, air-spaces, sap-receptacles, glands and vascular bundles are noticed; here certainly the fact has been overlooked that vascular bundles may be co-ordinated with epidermal formations, but not air-spaces, sap-receptacles and glands. His last chief division gives an account of tissue-systems and of the way in which the vascular bundles are united together in different plants, and secondary growth in thickness and the activity of the cambium-layer are described quite in the right connection.