480 Prof. H. Karsten on the Formation, 
der Entw. des Pollens, 1844) having published his observa- 
tions upon the formation of the pollen-cells, Mohl felt himself 
compelled, as a result of his repeated investigations of cell- 
formation, to assume, like Mirbel and Unger, that, in the deve- 
lopment of spores and pollen-cells, the division of the cell by 
constriction is combined with free-cell-formation (Vegetab. Zelle, 
1851, p. 220). 
In my investigations on the organic cell I included the deve- 
lopment of the pollen-cells of plants of different families; and 
the results arrived at differed from all others in these material 
points :—that the pollen-cell, which consists of a complex system 
of endogenous cells, is developed freely within the pollen mother 
cell; that the membranes of the numerous cell-nuclei and 
nuclear corpuscles contained in the pollen mother cells become 
themselves extended as the coverings of the pollen-cell, a new 
vesicle, which enlarges to form the nucleus, being formed in 
them, and in this again the nuclear corpuscle makes its appear- 
ance as a microscopic vesicle ; so that the origin of the nuclear 
corpuscles does not precede the formation of the membrane of 
the nuclear cell, nor is the production of the pollen-cells de- 
pendent upon an antecedently formed cell-nucleus. (De Cella 
vitali, 1843, p. 37, tab. 1 a—.) 
However, I was not at that time prepared to encounter the 
various scruples and objections which these opinions called 
forth ; consequently the brief statement then put forth, and the 
simple nature of the illustrations given, did not suffice to meet 
those objections. 
Indeed it is a very difficult matter to deduce the law of cell- 
formation from the history of the development of pollen, inas- 
much as these cells, in the course of their development, are 
more filled than others with opake material, and consequently 
their growth cannot be made the subject of direct observation, 
but the course of development must be gathered from a com- 
parison of many specimens. Hence it is that the observer is in 
this case more exposed to error than with the simple cellular 
plants. 
Still it seems to me that we must not pass over this much- 
debated and still imperfectly elucidated subject; and I will 
rather endeavour to prove, from what seems to me the most 
difficult object of investigation (which indeed most illusively 
represents the phenomena of constriction and fold-formation), 
that even the processes here taking place may be explained in 
accordance with the general law of free-cell-formation. I refer 
to those pollen-cells of Dicotyledonous plants whose primary 
cells (special mother cells-of Nageli), as also the membranes of 
their mother cells, become much thickened and often laminated — 
