3^0 Theory of Cell-formation [Book ii. 



statement that the nuclei are formed after the division. It is 

 surprising that after these considerations von Mohl thought that 

 his own observations necessarily confirmed Schleiden's theory of 

 cell-formation, although he noticed beside that the nucleus 

 never forms a part of the cell-wall, an essential feature in that 

 theory ; but in fact von Mohl took the membrane which accord- 

 ing to Schleiden separates from the nucleus for the primordial 

 utricle. But these mistakes are soon followed by the right 

 conjecture, that the substance of the primordial utricle may be 

 identical with the mucilaginous mass, which commonly encloses 

 the nucleus, and so with that which von Mohl two years later 

 named protoplasm. In this later treatise (' Botanische Zeitung/ 

 1846), in which he proves that the well-known movements in 

 the interior of cells are made not by the watery cell-sap but by 

 the protoplasm, he states (p. 75) that it is the protoplasm which 

 produces the nucleus, that the organisation of the nucleus 

 ushers in the formation of the new cell, and that contrary to 

 Schleiden's theory the protoplasm completely envelopes the 

 nucleus, which always occupies the centre of very young cells, 

 as is the case especially in the endosperm-cells observed by 

 Schleiden. He then shows how the protoplasm of young cells, 

 at first solid, afterwards forms sap-cavities and stretches between 

 them in walls, bands or threads, the substance of which exhibits 

 the streaming movement. Von Mohl strangely neglected on 

 this occasion to compare carefully his former observations on 

 the origin of spores and the division of Alga-cells with his new 

 results, and to seek for the essential resemblances between 

 them ; on the contrary he said emphatically that the cell-division 

 in Cladophora is probably a quite different process from the 

 multiplication of tissue-cells in higher plants. 



The discoveries of Unger and von Mohl up to the year 1846 

 were quite sufficient to refute Schleiden's theory, but not to 

 give a clear and general view of the processes in the formation 

 of cells ; the different kinds of cell-formation were neither 

 carefully distinguished from one another, nor could they be 



