186 PLANT MORPHOLOGY 



elongated and relatively little of the embryonic tissue becomes sporoge- 

 nouH (Fig. 152). The embryogeny is known only in a few species. The 

 lower cell arising from the first transverse division of the fertilized egg 

 may become an appendage to the foot in some forms but not in others. 

 Elaters are always present, but there is no elaterophore, except in Gott- 

 schca, which has a basal one. The spore mother cells are conspicuously 

 f our-lobed. The capsule wall is usually two layers thick, sometimes more, 

 the inner layer generally having spiral thickenings. Dehiscence occurs 

 by means of four valves, as in the Anacrogynae. 



Summary. In contrast to the Marchantiales, the Jungermanniales 

 have a gametophyte that, while remaining simple in structure, is more or 

 less differentiated in form. In the lower members the gametophyte is a 

 simple thallus, becoming in the higher members a leafy stem. The apical 

 cell is dolabrate in most of the Anacrogynae, tetrahedral in the Acrogynae. 

 In the Anacrogynae the sex organs are nearly always borne singly or in 

 groups on the dorsal surface of the gametophyte, sometimes on special 

 branches, but never on stalked receptacles. In the Acrogynae the anther- 

 idia are axillary, the archegonia terminal. The early development of the 

 antheridium is characteristic, the formation of two transverse walls in the 

 initial cell being followed by a median vertical wall in the terminal seg- 

 ment. The neck of the archegonium shows five cells in cross section. 



The sporophyte always consists of a foot, seta, and capsule. There is 

 much sterilization of potentially sporogenous tissue, the development of 

 the seta being especially marked. The capsule, varying in form from 

 spherical to cylindrical, produces both spores and elaters. It nearly 

 always dehisces by means of four valves. The capsule wall consists of 

 two or more layers of cells. The spore mother cells are deeply f our-lobed. 

 In the Jungermanniales a relatively simple gametophyte is combined with 

 a complex sporophyte. 



4. Anthocerotales 



The Anthocerotales constitute an isolated order of 4 genera and over 

 100 species. They are so distinct that they are often set apart from the 

 other liverworts as a distinct class of bryophytes. Anthoceros, with 60 

 species, and Notothylas are widely distributed in both temperate and 

 tropical regions, while Megaceros and Dendroceros are chiefly confined to 

 the tropics. Dendroceros is epiphytic on tree trunks, stems, and leaves, 

 while the other members grow mainly on damp earth. 



Gametophyte. The gametophyte of the Anthocerotales is a dorsi- 

 ventral plate-like thallus often growing in an irregularly dichotomous 

 manner (Fig. 153). It is frequently more or less lobed, but does not have 

 any leaves. In Dendroceros the thallus is narrow, consisting of a thick- 

 ened midrib and lateral wings composed of a single layer of cells. In the 



