REJUVENESCENCE IN NATURE. 227 



tents is combined with a division of them, a multipli- 

 cation of the cell takes place, constituting the basis of the 

 formation of tissues in plants where the cells remain 

 connected together, multiplication of the individual 

 where they separate. The various modes of origin of new 

 cells, which appeared so different and irreconcileable at 

 first sight, now all come together finally as cases merely 

 differing in degree of an essentially identical process, the 

 re-shaping of the cell-contents. The idea of origin of cells 

 outside, between or on the surface of existing cells, 

 formerly advocated by Mirbel, has proved untenable ; 

 neither the vegetative development nor the propagation 

 of plants exhibit anything but production of new cells 

 by transformation of pre-existing ones. 1 * This has been 

 called propagation of cells, but it must be observed here, 

 that in the majority of cases the entire contents, i. e. the 

 whole active living organism of the cell, passes directly 

 into the new structure, so that nothing remains behind, 

 unchanged, of the old cell (the mother-cell), except the 

 passive membranous wall. The daughter-cells are there- 

 fore not to be considered as young produced by the 

 mother-cell, existing contemporaneously with it, nourished 

 by and gradually developed in it, but as the rejuvenised 

 and metamorphosed mother-cell itself, f This is most 

 strikingly evident in those cases where the entire and 

 undivided cell-contents become loosened from the mem- 

 brane of the mother-cell, and, shaping themselves in a 

 different way, become a new cell : as is the case, for 

 example, in the formation of gonidia and spores in 

 (Edogonium, Bulbochtete, &c., and in the formation of the 



* Further researches are required to decide the relation of the in many 

 respects enigmatical formation of the yeast-cells, (the first cells of the 

 fermentation fungus,) and other analogous cases of what is termed generatio 

 spontanea, to cell-formation in the normal course of development and pro- 

 pagation of plants. (See Schleiden, ' Grundz./ 2d Aufl. 1, p. 203, ' Principles,' 

 pp. 36, 569, t. i, fig. 9, and Karsten, ' Urzengung, Botanische Zeitung,' 

 1848, p. 457.) 



f I cannot enter at length into the opposite view of Karsten, (' De Cella 

 Vitali,' 1844,) but I may remark that so far as relates to cell-formation it 

 totally contradicts my experience. 



