Robert Brown had already discovered the cell-nucleus; Schleiden recognised its more constant presence, but misunderstood its relation to cell-formation; Nägeli and von Mohl next demonstrated the peculiar nature of protoplasm, the most important component of vegetable cells, and especially the weighty part which it plays in their origination. Unger in 1855 called attention to the great resemblance which exists between the protoplasm of the vegetable cell and the sarkode of the more simple animals,—a discovery which was subsequently brought into prominence by observations on the behaviour of the Myxomycetes, and after 1860 finally led zootomists as well as phytotomists to the conclusion, that protoplasm is the foundation of all organic development, vegetable and animal. But there is yet another direction in which the study of the history of development by the phytotomist led to new points of view and to new results; we have already pointed in the end of the first book to the way in which Nägeli after 1844 made the sequences of cell-division in the growth of organs the basis for his morphology, and how in this way the Cryptogams especially revealed their inner structure; we also noticed the splendid results which Hofmeister achieved by his study of the development of the embryo; here we have further to show, how after 1850 the various forms of tissue, especially the vascular bundles, were examined by observation of the history of their development, and how in this way botanical science has succeeded in explaining the inner histological connection between leaves and axes, shoots and parent-shoots, primary and secondary roots, and above all in gaining a correct insight into subsequent growth in thickness and so learning to understand the true mode of formation of a woody body and of the secondary rind. It is then the task of the following chapter to give a more detailed account of the history of phytotomy, the salient points in which have now been indicated. CHAPTER I. PHYTOTOMY FOUNDED BY MALPIGHI AND GREW. 1671-1682.