STRUCTURE.] NAGELl'S THEORY. 35 



In no vegetable cells has it yet been, or probably ever will 

 be, demonstrated, that the nucleus is absolutely wanting. 

 On the contrary, wherever observation has been possible, it 

 has enabled us to recognize one. If, therefore, it is ever per- 

 missible to draw a conclusion from analogy, it must be so 

 here, and lead to the decision that the nucleus is an univer- 

 sal and unexceptional phenomenon in vegetable cells. This 

 assumption is so much the more justifiable since it does not 

 merely conclude from nine-tenths as to the remaining tenth, 

 but altogether from like to like. For there is no special 

 kind of cell, in which an example of the nucleus has not 

 already been demonstrated, while, in regard to all cells where 

 it has not yet been seen, individuals of the same kind are 

 known which possess it. 



" Cell-nuclei are primary or secondary, according to the 

 epoch of their origination. They have a perfectly distinct 

 relation to the \ital process of the cell. The primary nuclei 

 precede the cell; they make their appearance first in the 

 parent cell, and determine the formation of the progeny cells. 

 They exhibit two kinds of relation of position. That of the 

 first is where the primary nucleus lies free, and more or less 

 in the centre of the cell, which has been produced by its 

 influence. This is the case in the vegetative cells of all true 

 Fucoids and some green Algae (Conferva bombycina, Spiro- 

 gyra, Closterium, &c.), and in the special parent cells of all 

 plants which produce four spores or pollen grains in one 

 parent cell. (Floridese, Hepaticse, Musci, Filices, Lycopo- 

 diacese, and Phanerogamia) . The secondary kind of primary 

 nuclei are attached upon the wall of the cell which they pro- 

 duced. Such nuclei are possessed by all cells (with the 

 exception of the special parent cells) of those plants which 

 produce four spores in a parent cell (Phanerogamia, Lyco- 

 podiacese, Filices, Musci, Hepaticse, and Floridese) ; also the 

 cells of Equisetacese and Characese ; lastly, the cells of some 

 Algae (Arthrodesmus, Gaillionella, Bangia), and numerous 

 Fungi, 



" The secondary nuclei make their appearance in the cell at 

 a later period; they do not serve to produce new cells, but 

 are, apparently, at once the expression of an exalted vital 



D 2 



