THE HIGHER CRYPTOGAMIA. 125 



surface of the newly developed portions. In cases where 

 obliquely incident light intersected the smaller diameter of 

 the inverted gemmae, the younger portions of the latter 

 bent themselves simply backwards, so that the original 

 upper side was again turned to the light, and only rested 

 upon the soil by the one reflexed end. 



The under side, which by inversion had become directed 

 upwards, never developed stomata, not even at the points 

 directly exposed to the light ; on the other hand, when 

 kept in the shade and sufficiently moist, it sent out roots 

 in every direction, and as it advanced in age exhibited pro- 

 minent ribs (1. c, p. 355). Mirbel thought that the cell- 

 multiplication in the interior of the gemma?, was an inter- 

 polation of new cells between those already present (1. c, 

 p. 352). He has not discussed in detail the mode of rami- 

 fication of the Marchantieae, although the inquiry into this is 

 closely connected with the investigations as to the mode of 

 development of the gemmae. Even at a still later period, 

 up to the present time, this ramification has generally been 

 described as dichotomous (as, for instance, by Nees v. 

 Esenbeck, ' Naturgesch. Europ. Lebermoose ' iv, (1S38) 

 p. 83), whereas, in point of fact, it represents a Dichasium. 

 We are indebted to Mirbel for very accurate accounts of 

 the structure of the developed fructification, especially of 

 the relation of the longitudinal forks of the stem, which are 

 traversed by the rootlets, to the pileate expansion which 

 bears the reproductive organs (1. c, pp. 346, 376). Mirbel 

 was least successful in his investigations of the structure 

 and development of the organs of sexual reproduction ; his 

 figures are certainly beyond all comparison more elegant 

 and satisfactory than those of Schmidel and Hedwig, but 

 in the knowledge of the more important circumstances he is 

 not really a step in advance of the observers just named 

 (1. c, pp. 377 381). Mirbel's investigations of the develop- 

 ment of the spores and elaters were of great scientific im- 

 portance, the more so because, in conjunction with Mold's 

 contemporaneous works on the same subject, they gave an 

 impetus to the more accurate investigation of the visible 

 processes of cell-formation and cell-multiplication. Mirbel 

 pointed out the division of the contents of the spore-mother- 



