Page:History of botany (Sachs; Garnsey).djvu/346

326 doctrine, and his observations on the punctum vegetationis appeared in the 'Linnaea' of 1841, p. 389; from the size and position of the cells he concluded that the tissue-cells in this case are formed by division, and not in the manner alleged by Schleiden. Soon after Nägeli also ('Linnaea,' 1842, p. 252) observed the processes of cell-formation in the extremities of roots, but he did not conceive them to be cases of division; he saw two nuclei form in each mother-cell, and a new cell form round each nucleus, and explained the origin of the dividing wall as due to the meeting together of the two new cells; he thought that a similar process takes place in stomata and in the mother-cells of pollen; this conception was not absolutely incompatible with Schleiden's theory, but there was this difference, that in Nägeli's case essential processes were correctly observed, but were to some extent incorrectly interpreted. In the same year appeared the first edition of Schleiden's 'Grundzüge der wissenschaftlichen Botanik,' in which his theory of cell-formation was repeated in a more precise form. That he was thoroughly in earnest to maintain it is shown by the fact that he gave still another exposition of it in his 'Beiträge zur Botanik' in 1844, where he insists that his method of cell-formation is the general one, though it has been distinctly ascertained in the Phanerogams only. But how completely an observer may be led captive by a preconceived opinion may be learnt from Schleiden's suggestion, that the formation of zygospores in Spirogyra is in accordance with his views, though it