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 according 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