CHAP, iv.] from 1838 to 1851. 325 



cambium, begins as a minute vesicle, and grows to the size 

 which it reaches in its matured state. The resemblance of this 

 view to that of Sprengel and Treviranus is increased by what we 

 find further on, where we read that from the cell-germs in the 

 spores of Marchantia usually only from two to four serve to 

 form cells, the rest becoming overlaid with chlorophyll, and 

 being consequently withdrawn from the vital process. He who 

 is acquainted with the modern view of the processes of free 

 cell-formation founded on the numerous and careful investiga- 

 tions of later times will scarcely discover in the above account 

 of Schleiden's theory a single correct observation. 



Soon after, von Mohl published in ' Linnaea,' 1839, p. 272, 

 his observations on the division of the mother-cells of the spores 

 of Anthoceros ; these were carefully made and were correct in 

 all the main points ; and in opposition to Mirbel's former state- 

 ments they establish the fact, that the division is effected by 

 the mucilaginous contents of the cell, and consequently that it 

 is not a passive division of the contents of the mother-cell pro- 

 duced by the growth inwards of projections of the cell-wall. 



Unger * was the first to declare distinctly against Schleiden's 



1 Franz Unger was born in iSoo on the estate of Amthof, near Leut- 

 schach in South Steiermark, and was educated up to the age of sixteen in 

 the Benedictine Monastery of Gratz. Having gone through the three years' 

 course of ' philosophy,' he turned his attention, by his father's wish, to juris- 

 prudence; but he abandoned this study in 1820, and became a student 

 of medicine, first in Vienna, and afterwards in Prague. From the latter 

 place he made a vacation tour in Germany, and formed the acquaintance of 

 Oken, Carus, Rudolphi, and other men of science, and in 1825 of Jacquin 

 and Endlicher, with the latter of whom he maintained an active corre- 

 spondence on scientific subjects. Having taken his degree in 1827, he 

 practised as a physician in Vienna till the year 1830, and after that date 

 was medical official at Kilzbuhl in the Tyrol. During these years he 

 continued the botanical studies which he had commenced as a youth, and at 

 Kitzbiihl directed special attention to the diseases of plants, to palaeonto- 

 logical researches, and to enquiries into the influence of soil on the distribu- 

 tion of plants. At the end of 1835 he became Professor of Botany at the 

 Johanneum in Gratz, and devoting himself there especially to the study of 



