270 BRYOPHYTA 
to have the intercalary activity unlimited. Moreover, in these small 
sporogonia, though a sterile columella is often present, sometimes its 
place is taken by fertile tissue; and the difference may be seen in sporo- 
gonia of the same species. The details of this were long ago described 
by Leitgeb,! but doubts have since been raised regarding his conclusions by 
investigators who, working chiefly with other species, did not obtain the 
same results.2_ Recently, however, Lang has made observations which go 
far to explain the discrepancies; and though they do not exactly coincide 
with Leitgeb’s account as regards the development of /Vofor/hylas, they show 
that, as regards the fertility of the columella, he was substantially correct.3 
It appears that the embryonic structure of the sporogonium of 
Notothylas is essentially like that of Amthoceros, in respect of the relations 
at its base of columella, archesporium, and capsule-wall. In those cases 
where the columella is present in the mature state, the spore-mother-cells 
originate only from the archesporium. But in other cases where a definite 
columella is not present in the mature state, any cell of the tract laid 
down structurally as columella may become a spore-mother-cell. Many 
do so, and thus, as Leitgeb described, the place of the sterile columella 
may be taken by a spongy mass of sterile tissue, in the meshes of which 
the spores are included. In addition to this, however, fertile cells and 
elaters are also produced from the archesporium, which lies, as in 
Anthoceros, outside the columella (Figs. 131 a-F). Two interpretations 
of this state are possible: either that the columella-less forms are primitive, 
and their partly fertile condition intermediate towards the establishment 
of a completely sterile columella: or that the forms with a columella are 
primitive, and the columella-less forms a reversion, some of its cells 
resuming fertility which had previously been lost. Dr. Lang is inclined 
to consider the columella-less forms as reduced: but whether reduced or 
not the facts throw considerable light upon the relation of the columella- 
less to the columelloid forms: they increase the justification for considering 
the central group of cells, which in all other Anthocerotaceae is wholly 
devoted to the formation of a sterile columella, as the original sporogenous 
tissue, and the amphithecial archesporium as of secondary origin. The 
duty of producing spores would seem to have been transferred from the 
central to the superficial set of cells. It is thus possible to bring the 
apparently divergent sporogonium of the Anthocerotales into relation to 
that of the simpler and probably more primitive Jungermanniales. The 
causes of the change of the products of the endothecium from the fertile 
to the sterile condition must be looked for in influences acting on the 
primary meristematic tissue of the embryo, or on the intercalary zone of 
secondary meristem. Dr. Lang holds* that the idea of grouping of elaters 
in a central position to form the columella is not in this case in accordance 
1 Lebermoose, V., p. 39. 
2 Mottier, Bot. Gaz., 1894; Campbell, Mosses and Ferns, Edn. ii., Pp. 151-155. 
“Lang, Ann. of Bot., vol. xxi., p. 201, etc. 4Z.c., p. 208, 
