212 



BOTANY 



The Jungermanniales are divided into two suborders, the Anac- 

 rogynae, or Metzgeriaceae, aud the Acrogynae, or leafy Jungermanni- 

 aceae. In the former, the archegonia are dorsal, 

 and never arise directly from the apex of the 

 shoot ; in the Acrogynee, the apex of the arche- 

 gonial shoot becomes transformed into an arche- 

 gonium, and its longitudinal growth is thus 

 stopped. 



Suborder I. J. Anacrogynae 



The anacrogynous Jungermanniales are of 

 especial interest, as they represent, on the 

 whole, the simplest type of the Archegoniates, 

 and one suggesting the ancestral form from 

 which the more specialized types have been 

 derived. Among the Anacrogynse are many 

 interesting transitional types. The lowest 

 forms have a delicate thallus growing from a 

 two-sided apical cell, and closely resemble the 

 younger stages of many of the higher Arche- 

 goniates, which may be traced back to such a form. The early 

 stages of such Liverworts as the Marchantiaceae, and the young 

 gametophyte of most Ferns, usually conform to this type. Some of 



D. 



m. 



FIG. 170. Marchantia 

 polymorpha ; tuber- 

 culate rhizoid ( X 525). 



B 



FIG. 171. A-C, Riccia glauca. D, R. trichocarpa. A, B, longitudinal, C, trans- 

 verse, sections of young embryo (X 260). D, an older embryo, showing the layer 

 of sterile cells, m, surrounding the sporogenous cells (X 220). 



