101 



(2) JUNGERMANNIALES 



General character. This is by far the largest group of liverworts, its 

 members living in all conditions of moisture from very wet to very dry. 

 They are especially abundant in tropical 

 forests, being very common on the bark of 

 trees (epiphytic) and on leaves (epiphyllous), 

 while some grow on the ground. Two great 

 groups are recognized : (i) thallose forms, 

 whose gametophyte body is a thallus resem- 

 bling that of the Marchantiales in general 

 outline (see fig. 777); (2) foliose forms, with 

 leafy bodies (fig. 235). However, there is FIG. 23 i.-P^ia: thallus 



, . , . . . i j. bearing a sporophyte with 



complete gradation from thallus bodies, long seta (indicating also 

 through those whose thallus is more and position of archegonium) ; 

 more deeply lobed, to those in which the the black dots on the older 



. , . .. . . portion of the thallus in- 



lobes have become distinct leaves. dicate antheridia . 



The most essential distinction between the 



two groups is based upon the position of the archegonia, which of 

 course involves the position of the sporophytes. In the thallose forms 

 the archegonia are on the dorsal surface of the thallus (figs. 231, 232); 



and on this account they are 

 called the Anacrogynae, mean- 

 ing archegonia not at the apex. 

 In most foliose forms the apical 

 cell becomes an archegonium 

 initial; and on this account they 

 are called Acrogynae, meaning 

 archegonia at the apex (fig. 235). 



The acrogynous Jungerman- 

 FIG. * 3 *-Symphyogyno.' thallus showing ^^ ^ knQwn comrnonly as 

 lobed margin and bearing two sporophytes on 



its dorsal surf ace. the leafy liverworts, or some- 



times as scale mosses. 



In contrast with the Marchantiales, the Jungermanniales show very 

 little differentiation of the tissues of the gametophyte; but they show 

 very great differentiation in the form of the gametophyte. 



(a) Anacrogynae 



Gametophyte. The gametophyte of the simplest Anacrogynae, 

 such as Aneura and Pellia, are the simplest gametophytes known among 



