Anthocerotales. 
343 
gummy liquid. Indeed all the tissues contain abundant mucilage, 
which escapes when the thallus is cut into. 
The thallus shows two vegetative features of special interest, 
the peculiar chloroplasts and the Nostoc- cavities. In nearly every 
cell there is, in most species of Anthoceros, a single large 
chloroplast, varying in form, but usually oval and flattened, with a 
conspicuous central pyrenoid, around which starch-grains are 
clustered as in various Green Algae with similar chloroplasts. 
The nucleus lies in close apposition to the chloroplast, usually near 
the pyrenoid, and sometimes the chloroplast becomes folded so as to 
enclose the nucleus more or less completely. The curious Nostoc- 
cavities almost always found in the lower tissue of the thallus were 
described by Hofmeister (13), who mistook them for gemmae ; what 
he figures as cell-walls dividing up the cavity are in reality the 
hairs which grow in from the cells bounding the chamber after the 
Nostoc has entered by means of a slit between two of the lower 
superficial cells of the thallus. The real nature of these cavities 
was discovered by Janczewski (17) and Szymanski (34), while 
Leitgeb (22) carefully followed the development of the cavities and 
their infection by the hormogonia of Nostoc and showed how the 
Nostoc- chains grow vigorously in the enlarging cavity, the cells 
lining the latter growing into hairs which mingle with the alga. 
These cavities are primarily gum secreting organs, and Peirce (30) 
has recently shown that Anthoceros plants raised from spores in 
sterilised soil grow quite normally, and probably even better, in the 
absence of Nostoc. 
Apart from Hofmeister’s “ gemma,” which turned out to be 
the Nosfoc-cavities just mentioned, there are some observations 
on record which seem to indicate that Anthoceros has special 
organs for asexual propogation. Hofmeister’s account of small 
gemma which arise by rejuvenescence of the mother-cell and 
escape through a pore in the wall does not appear to have been 
confirmed, though gemma, or more correctly gonidia, of this nature 
occur in Aneura and Metzgeria. Ruge (31) has described and 
figured the development in Anthoceros glandulosus of stalked brood 
bodies which have a mucilage cavity and pore already formed 
before being detached from the parent plant. 
The sexual organs of the Anthocerotales differ very markedly 
in certain respects from those of other Bryophytes, though their 
peculiarities have been somewhat exaggerated by some writers. 
In the case of the antheridia, either one, or (in Notothylas and 
