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-i.) 



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 



