REJUVENESCENCE IN NATURE. 235 



halves; and Hofmeister,* in addition, directs attention 

 here more particularly to the primordial utricle, bounding 

 and cutting off the two parts from each other, even 

 before the origin of the cellulose dissepiment. 



According to this representation, the septum is formed 

 by the two individualised portions of contents into which 

 the mother-cell divides, and which secrete cellulose upon 

 their whole surface after they become separately consti- 

 tuted, touching by their flat adjacent surfaces; whence of 

 course the cellulose layers formed on the surfaces of 

 contact become united, and thus form what appears a 

 simple septum, which, however, from the nature of its 

 origin, is composed of two plates, standing in unbroken 

 connection with the other parts of the new cellulose lining 

 which coats the sides of the cell turned towards the wall 

 of the mother-cell. Referring to the ab origine existing 

 contact of the daughter-cells with the whole internal 

 surface of the wall of the mother-cell, in formation of 

 cells by division of the whole contents, Nageli calls the 

 formation of cells by division ''Parietal cell-formation'' 

 Under the hypothesis that the contents become com- 

 pletely divided before the formation of the septum, he 

 regards the latter as simultaneous through its whole 

 extent. In contradiction to this last assertion, Mohlf 

 describes in Confervse, particularly in Conferva (Clado- 

 phora) glomerata, a cell-formation taking place by gradual 

 constriction of the cell-contents, in which the formation of 

 the new layers of cell-membrane begins, before the com- 

 pletion of the division, over the whole surface of the 

 primordial utricle, and, since it penetrates the fold which 

 the primordial utricle forms at the place of constriction, 

 causes the formation of a septum penetrating gradually 

 from the circumference to the centre. In another place, \ 



* ' Die Entstehung des Embryo der Phanerogamen,' p. 1 ; ' Ueber der 

 Eiitwicklung des Pollens,' (Bot. Zeit., 1848, p. 655.) 



f ' Ueber die Vermekrimg der Pflanzen-zellen durch Theilung,' (Ver- 

 mischte Schriften, 1845, p. 362.) 



J ' Eiiiige Bemerkungen liber der Bau der Vegetabilischeu Zelle,' (Bot. 



