Between 1840 and 1850 the most eminent representatives of phytotomy were chiefly engaged, as we have seen, in observing the formation of vegetable cells, and in framing the true theory of the subject by process of induction. It was not to be expected that, while these labours were bringing year by year new things to light and keeping opinion on the formation of cells in a constant state of fluctuation, their results would lead to very important changes in the theory of the solid framework of cell-membrane founded by von Mohl. On the contrary, it was at this time that his views such as we have seen them on the connection of cells one with another, on the configuration of their partition-walls and on their growth in thickness, attained their greatest influence. His theory seemed to stand firm and complete when contrasted with the unsettled state of opinion respecting the origin of cells, and the question, how far it could be made to agree with the new observations on the history of cell-formation, was hardly raised. In the midst of the strife of opinion on the latter subject appeared von Mohl’s ‘Vermischte Schriften’ in 1845, in which his views on the structure of mature vegetable tissue were produced in a series of monographs as the apparently irrefragable result of his observations. And in fact phytotomic research up to 1860 followed the train of thought initiated by von Mohl, till at last the inadequacy of his views was rendered apparent between 1858 and 1863 by Nägeli’s new theory of growth by intussusception, and by the profounder insight obtained into the nature of cell-formation.