508 Campbell . — The Development of 
highly developed sporogonium with its long seta and true 
elaters. The growth of the thallus is from a two-sided apical 
cell ; the sexual organs are destitute of a special envelope ; 
the divisions in the antheridium are those of the typical 
Jungermanniaceae; and the neck of the archegonium has five 
peripheral rows of cells. 
Petalophyllum , according to Leitgeb 1 J agrees closely with 
Fossombronia in its apical growth and in the development of 
its leaves. The antheridia are partially surrounded by an 
imperfect envelope, but the archegonia are in groups. An 
interesting resemblance between P etalophyllum and Geothallus 
is the formation in the former of bulb-like structures, probably 
similar in nature to the tubers of Geothallus. This is asso- 
ciated with the burying of the thallus in the sandy soil where 
the plant grows 2 . 
All of the Anelatereae show unmistakable resemblances 
to the lower Marchantiaceae, especially Riccia , and are 
probably pretty near the point at which the Marchantiaceae 
and Jungermanniaceae diverge. Sphaerocarpjis is on the 
whole the most primitive type, and Geothallus may be said 
to be an intermediate between it and forms like Fossombronia . 
This is indicated both by the structure of the antheridium 
and the leaves. The development of leaves, however, cannot 
be considered as being very important as bearing upon its 
relationship with other forms, since this has occurred beyond 
question at several points in the series of Anacrogynae. It 
emphasizes, however, the exceedingly generalized and pre- 
sumably primitive character of the whole group, and its im- 
portance in a study of the origin of the higher Archegoniates. 
1 Leitgeb, 1 . c., iii. p. 130. 
2 Ibid. p. 126, footnote. 
