Von Mohl’s dissertation on the multiplication of vegetable cells by division, published in 1835 and reprinted in ‘Flora’ of 1837, shows how strange these processes even then appeared; in this work he expresses some doubts about Mirbel’s statements, but he accepts them on the whole, and only makes incidental mention of his own more numerous and better observations on the development of spores (‘Flora,’ 1833), though he had there seen several cases of cell-division and free cell-formation with tolerable distinctness. Adolph Brongniart (‘Annales des sciences naturelles,’ 1827) also had observed, though imperfectly, the formation of pollen-grains in their mother-cells in Cobaea scandens, and Mirbel, in the appendix to the work mentioned above, had given a correct description and good figures of the formation of pollen-cells; and yet von Mohl neglected to compare these important observations of cases of cell-division with his own; even in 1845, when he published the latter in a revised form in his ‘Vermischte Schriften,’ he overlooked the close relation between the formation of those pollen-grains and spores, and the cell-division in Cladophora. Still this treatise of von Mohl’s is of great importance in the history of the theory of cell-formation, because it described a case of cell-division for the first time step by step and brought all the salient points into relief. Dumortier had observed the division of cells as early as 1832[86], and Morren had seen it in Closterium in 1836, but had not given the needful details. Finally, von Mohl applied the experience which he had gained from Cladophora to other filamentous Algae, and pointed out the similarity between these processes and the division of Diatoms, which he consequently claimed as plants in opposition to Ehrenberg, who considered them to be animals (‘Flora,’ 1836, p. 492).