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 'Anatomic und Physiologic 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.
In this branch of the science, as in every case where it is a question of establishing fundamental conceptions, of surveying facts from extensive points of view, and of seeking the requisite principles by means of the history of development, we find that it is Nägeli who opens the way and lays the foundation. In his 'Beitrage zur wissenschaftlichen Botanik' of 1858, he proposed a classification of tissues from purely morphological points of view. His first division was into generating and permanent tissue; in each section he distinguished two forms, prosenchymatous and parenchymatous tissue. Parenchymatous
