Development, and Structure of the Vegetable Cell. 483 



It is this state of things which especially caught the attention 

 of former observers, and which they represented as constituting 

 the first indications of the special pollen-cells. 



Unger (Merisraatische Zellenbildung bei der Entwickelung 

 des Pollens, 1844) thus refers to the subject: — ''At first some 

 thin delicate striae make their appearance within the mother cell, 

 which can, by making the cell revolve, be proved to be nothing 

 else than transparent walls which divide the granular mass into 

 several portions. They are so fragile that they dissolve in 

 water." 



These statements of Unger are entirely correct, supposing 

 that the word " first " applies to the ready formed septa ; but 

 even in this condition the delicate membranes appeared to me 

 in the end to yield to the solvent energy of the water. 



And in fact, if we will not call in the aid of analogy in the 

 interpretation of the phenomena, it seems impossible to prove 

 that those free cells enveloped by the plasma within the pollen- 

 mother cell and apparently soluble in water, and which may be 

 recognized of different sizes within the unequally developed 

 pollen mother cells of the same anther, form, by the mutual ap- 

 position of their enlarged membranes simultaneously with the 

 assimilation of the plasma, the line-like and exceedingly deli- 

 cate septa (whose double nature can very rarely be detected), by 

 which, in a subsequent stage of development, the turbid cell- 

 juice of the pollen mother cell is subdivided. 



The conditions here prevailing do not allow, as in (Edogonium, 

 of the actual and continuous observation of the growth of the free 

 endogenous cells, the assimilation of the cell-juice enveloping 

 them, and the formation and increase of their contents. Never- 

 theless I consider that we are perfectly justified in inferring, 

 from a certainly recognized fact, the occurrence of another 

 similar one, although the latter cannot be observed with the 

 same certainty ; and I therefore assume that even the delicate 

 septa, which at a certain stage of development divide the pollen 

 mother cells, are the walls of those free cells which may be de- 

 tected in them in other similar and earlier states. 



This opinion coincides with that of Mohl as expressed in his 

 first- quoted essay on the development of spores. 



Moreover in spores, just as in pollen mother cells, four free 

 cells are present, by the expansion of which so as to fully occupy 

 the mother cell the septa in all probability originate. 



That these septa are not simple, as supposed by Unger (be- 

 cause even in this very young state they cannot be split by the 

 application of diosmotic fluids), but that they consist of two 

 membranes belonging to two approximated special mother cells 

 of the pollen, was maintained even by Nageli, although he did not 



