REJUVENESCENCE IN NATURE. 153 



and whorl- formation which branches seern to arise, 

 inside the whorl-branches, from the link-cells of the 

 stem. 



Having seen, first, in the lowest stage, vegetation and 

 fructification united in a single cell; then, in a second 

 stage, a series of generations of vegetative cells, which, 

 however, pass in the last generation into fructification 

 in all the members ; finally, a step farther, first only a 

 few cells persisting as permanent vegetative cells, side by 

 side with the series of generations going out into fructifi- 

 cation, then a gradually and continually increasing 

 proportion of the successive generations of cells developing 

 into new vegetative supporters of the fructifying parts, 

 Batrachospermum at length displays to us a case of more 

 decided separation of an original series of generations of 

 cells destined to simple vegetative formation, and de- 

 duced or secondary series attaining fructification only in 

 certain terminal links. Nevertheless, comparatively speak- 

 ing, we are yet still among the simplest rudiments of the 

 differentiation and complication of the vegetable organism, 

 through the ever more variously divided and arranged suc- 

 cession of generations of cells, and the, at the same time, 

 ever increasing diversity of the conformation and physio- 

 logical activity of the individual cell. For a further advance 

 it becomes necessary to show how compound solid cellular 

 structures are formed from simple rows of cells, the link-cells 

 of the stem becoming the mother-cells of new, subordinate 

 series of generations, which divide according to new laws 

 of direction in the given space of the link-cell, separating 

 either into similar parts, as in Myriotrichia* and 

 Sphacelaria, or into dissimilar, by the formation of a 

 circle of cells around a central cell, as Polysiphonia.\ 

 It must be shown, moreover, how a distinction between 

 cortical and medullary tissue arises, through a further 

 continued division of the cells at the periphery of the 



* Nageli, ' Algeusysteme,' p. 147, t. iii, figs. 1319. 

 f Kiitzing, 'Phyc. generalis,' t, 1, f. 3. Nageli, ' iibcr Polysiphonia.' 

 (' Zcitschr.,' 1846, p. 207, t. vi and vii.) 



