Phytogeny of Marchantiales. i 77 
receptacle with a single anterior growing-point, no perianth, and no 
ring-fibres. 
The earliest stages in the development of the carpocephalum of 
the higher Marchantiales were first fully worked out by the writer 
for Fegatella (14); Preissia and Marchantia give similar results so 
far as these stages are concerned. When the formation of a 
carpocephalum is about to begin, the growing-point of the thallus 
broadens out and undergoes a first dichotomy, a “middle lobe” 
being formed between the two new growing-points exactly as in 
ordinary apical branching. Each of these growing-points becomes 
broadened and undergoes dichotomy. In Preissia branching stops 
at this stage, but in Marchantia polymorpha each of the four 
growing-points divides again, giving eight growing points ; in both 
genera each of the growing-points eventually produced gives rise to 
a series of archegonia. In the case of Fegatella only two of the four 
growing points divide again, as a rule, and each of the six growing- 
points usually produces only one archegonium. 
There is every reason for the belief that the carpocephala of all 
Marchantiaceae, excepting Clevea and Plagiochasina, will be found to 
show the “Composite” mode of development just described, and 
that the organisation of the fully developed carpocephalum will be 
found to depend upon differences in detail in the later stages of 
growth. Thus, the presence in the stalk of a single furrow or of 
two furrows probably depends upon differences in (1) the rapidity 
with which the early apical divisions succeed each other and (2) the 
amount of growth which occurs in the tissue at the base of the 
developing carpocephalum. The fact that repeated dichotomy of 
the apex has been demonstrated in the development of the carpoce¬ 
phalum of Fegatella, despite the fact that the archegonia are usually 
produced singly in the involucres—that is, one archegonium from 
each growing-point—certainly suggests that the carpocephala of all 
the Marchantiaceae, except Clevea and Plagiochasina, represent 
branch-systems, and that they differ only in such details as form, 
size, number of furrows in the stalk, presence or absence of 
projecting rhizoid-sinuses, presence or absence of perianths, number 
of archegonia produced by each growing-point. 
Leitgeb distinguished three types of carpocephalum in the 
Marchantiaceae : (1) the Clevea and Plagiochasina type, with furrow¬ 
less stalk, and one archegonium in each involucre; (2) the Opercu- 
late type, including the Astroporae, the Operculatae, and Fegatella, 
with a single groove (two in Peltolepis) and a single archegonium in 
