326 Theory of Cell-formation [BOOK 11. 



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 Nageli 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 differ- 

 ence, that in Nageli'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 ' Grund- 

 ziige 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 ( Beitrage 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 zygo- 

 spores in Spirogyra is in accordance with his views, though it 



palaeontology, he soon became the most eminent authority on that subject. 

 Having been made Professor of Vegetable Physiology in Vienna in 1849, 

 he applied himself more to physiology and phytotomy. He retired from 

 this position in 1866, and from that time forward lived as a private in- 

 dividual in Gratz, promoting scientific knowledge by the publication of 

 popular treatises and the delivery of lectures. lie died in 1870. Informa- 

 tion respecting his personal character and his varied and copious labours in 

 many departments of botanical science is given by Leitgeb in the ' Bota- 

 nische Zeitung' of 1870, No. 16, and by Reyer, ' Leben und Wirken des 

 Naturhistoriker Unger,' Gratz, 1871. 



