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 ‘Beiträge 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 generating tissue, the original component of every young organ, he named primary meristem as distinguished from prosenchymatous generating tissue, which is differentiated in the form of strands and layers, and received from him the general name of cambium; this was certainly not a happy distinction, because Nägeli’s cambium by no means consists entirely of prosenchymatous tissue. By the term secondary meristem Nägeli designated the tissue-strands and tissue-layers which are formed between the permanent tissue of older parts. The cambium he regards as the first product of the primary meristem. The second chief form, permanent tissue, he divides into two classes, not according to the form of the cells or physiological relations, but according to its origin; all permanent tissue, which is derived immediately from primary meristem, is protenchyma, all that comes directly or indirectly from cambium is epenchyma. And since the tissue-strands, till then known as vascular bundles, do not contain vessels only but always fibrous elements also, as Bernhardi had shown in 1805, Nägeli thought that they should therefore be called fibrovascular strands. If it cannot be denied that the obvious distinction between epidermal and other tissue did not find suitable expression in this classification, and though other points of view may at the present day be proposed for the genetic arrangement of tissues, yet Nägeli’s classification and terminology have the merit of having for the first time exhibited the general histology of plants on comprehensive and genetic principles. It contributed materially to impart a better understanding of the collective structure of plants. The vascular bundles or fibrovascular strands especially demanded further investigation of the genetic and morphological kind; for a correct insight into the origin and subsequent transformation of this tissue-system is as important for phytotomy as a similar knowledge with respect to the bony system in vertebrate animals is for zootomy. But a knowledge of the vascular bundles and their course in the stem has a special importance in phytotomy, because it is the only way to the understanding of secondary growth in thickness in true woody plants.