* 124 HOFMEISTER, ON 



the origin of the quadrangular stomate upon the vegetative 

 shoots is to some extent erroneous, for he assumed such 

 origin to lie in the disintegration of one four-sided cell, 

 surrounded by four epidermal cells, which (four-sided) 

 cell is, in reality, the mother-cell of the cells which enclose 

 the stomate, and which afterwards separate from one 

 another. H. von Mohl commented upon this error in the 

 ' Linnsea' (1838) and in his ' Vermischte Schriften/ p. 252. 

 Mirbel's representation of the origin of the stomate sur- 

 rounded by more than four cells is, on the other hand, 

 quite natural (1. c, p. 356). 



With regard to the receptacles of the gemmae, Mirbel 

 believed that, at the time of their appearance, the super- 

 ficial cellular layer of the flat stem became detached from 

 the underlying tissue, and separated into converging 

 teeth, which soon constituted the margin of the receptacle. 

 Mirbel has rightly apprehended the unicellular, earliest 

 state of the gemmae (1. c, p. 350) ; his notion of the con- 

 temporaneous metamorphosis of the contents of the uni- 

 cellular gemmse into a multicellular tissue filling the cell 

 was confirmed by Nageli in 1845 (' Zeitschrift f. wiss. 

 Bot./ ii, p. 150). Mirbel's investigations of the germina- 

 tion of the gemmse of Marchantia are of especial interest. 

 He showed that that surface of the gemmae which happens 

 to be in contact with the ground develops rootlets, whilst 

 the other one forms the upper surface by development of 

 stomata and air-cavities ; but that, twenty-four hours after 

 being sown, and when only a few rootlets have grown 

 out of the under side, the upper and under surfaces of 

 the future plant have already become permanently dif- 

 ferentiated. When gemmae, which had been sown for this 

 short period, were reversed, rootlets grew from that side, 

 which having been formerly the upper, had become the 

 UDder surface, whilst those rootlets which had sprung 

 from the quondam upper, then the under surface, con- 

 tinued to grow, and bending themselves downwards, pene- 

 trated the soil. During the further growth of the gemmae, 

 however, each of the elongating lateral halves effected a 

 semi-revolution around its axis, so that the surface which 

 had been formerly the upper one again became the upper 



