Anthocerotales. 
35i 
meristematic tissue above the haustorium of the sporogonium in 
Anthocerotales evidently results from the persistence of a stage 
which is quickly passed through in the development of the sporo¬ 
gonium in other Hepaticae. In Pellia, for instance, the cells of the 
seta are arranged in regular longitudinal rows, owing to repeated 
transverse divisions in the cells between haustorium and capsule, 
and we may imagine the sporogonium of Anthocerotales to have 
arisen through the persistence of the meristematic activity of this 
zone of tissue, the differentiation of the capsule being deferred and 
becoming basipetal, instead of taking place early and being simul¬ 
taneous. The columella of the Anthocerotean capsule, again, may 
be compared with the incomplete sterilisation of central tissue 
which results in the formation of the elaterophore of such forms as 
Pellia, Aneura, and Gottschea splachnophylla . It is doubtful 
whether much stress should be laid on the presence of stomata in 
the epidermis of the Anthoceros capsule; this feature is doubtless 
to be correlated with the development of a many-layered capsule- 
wall consisting of assimilative parenchyma. In various Junger- 
manniales, the capsule-wall is many-layered, and when young 
contains chloroplasts—a condition which persists in the Antho¬ 
cerotales, but is also found in the ripe capsules of forms like Riella, 
where the cells of the capsule-wall do not become thickened with 
fibres in connection with a special dehiscence mechanism. 
It seems probable that the Anthocerotales have arisen from 
forms like the Sphzerocarpales, along a well-marked line of develop¬ 
ment which has led no further, and which is marked mainly by the 
“endogenous” origin of the antheridia and by the retention of a 
basal meristematic zone in the sporogonium. The antheridia were 
doubtless originally exogenous, and instead of becoming surrounded 
by an envelope (as in Sphaerocarpales) or sunk in an open pit (as in 
Marchantiales and various Anacrogynous Jungermanniales), they 
have become sunk in a closed cavity formed by splitting of the walls 
between the antheridium-forming hypodermal cell and the surrounding 
thallus cells. The occurrence of a group of antheridia formed by 
longitudinal splitting of the young antheridium, is clearly a 
secondary character, just as is the process of budding which leads 
to the formation of more than four antheridia in a cavity in some 
species of Anthoceros. All the distinguishing characters of the 
Anthocerotean sporogonium are more or less definitely correlated 
with the persistence of the basal meristematic tissue, and are con¬ 
nected with the nutrition of the spores. The basal meristem 
