IIEJUVENESCENCE IN NATURE. 257 



rations (two and two). Hofmeister mentions the opposite 

 case as occurring in Tradescantia, in which the special 

 parent-cells are usually formed two and two (in one plane 

 or decussating), sometimes, however, all four simul- 

 taneously (in tetrahedral position).* This remarkable 

 circumstance indicates an intimate connection of the two 

 cases, to which we are still more definitely attracted by 

 certain observations on the behaviour of the nucleus 

 before the direct quartering. In the first place, we must 

 here recall the remarkable course of development of the 

 spores of Anthoceros, described by H. von Mohl,f and 

 also by Nageli.f At the sides of the central nucleus of 

 the mother-cell, here, as an exception, not vanishing, two 

 new nuclei are formed (called by Mohl, from their 

 granular contents, "granule-cells"), which after some 

 time divide, thus producing four nuclei, which, gradually 

 retreating from each other, assume a tetrahedral arrange- 

 ment. Around these four nuclei the special mother-cells 

 are simultaneously formed, by division of the entire 

 contents of the general mother-cell. Still more expressive 

 are the observations made by Hofmeister on the forma- 

 tion of the pollen of Pinus. ^ The large nucleus becomes 

 dissolved; two secondary nuclei are formed; between 

 these two the granules of the cell-sap accumulate as an 

 annular zone at the equator of the cell; the zone of 

 granules soon splits into two parallel zones, indicating 

 the separation of the primordial utricle into two halves. 

 Up to this point all the mother-cells behave alike, but 

 the subsequent development takes place in two different 

 ways. Either the indicated division into two primary 

 special mother-cells is carried out, and two secondary 

 special mother-cells are formed again in each of them ; or 

 the commencing halving of the primordial utricle is inter- 



* 'Bot. Zeit.,' ]848, p. 430, t. iv, f. 33—36. 



•j- ' Ueber die Entwick. der Sporen von Anthoceros Idevis,' (Linnsea, ] 839 ;) 

 ' Verm. Schrift.,' p. 84, t. iv. 



X ' Zeitsohrift,' 1844, pp. 49—54, t. i, f. 31—40. (Ray Transl., 1845, 

 pp. 239—333, t. vi, fig. 31—40.) 



§ ' Bot. Zeit.,' 1848, p. 671. 



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