266 
Notes on Recent Literature. 
deep narrow chambers arose according to the method described by 
Leitgeb. In reviewing this paper, Land (Bot. Gnz., Vol. 49, 191(3, 
p. 393) rightly pointed out that the authoress had not produced 
conclusive evidence either way, and that “ such investigations 
should he preceded by a careful study of the development of the 
thallus from the growing-point, and there should be a clear con¬ 
ception of the arrangement of the cells which result from this 
growing-point.” Petsch (31) has now made a thorough investigation 
of the air-chambers of the Ricciaceae, and has traced carefully the fate 
of the dorsal segments cut from the initial-cells of the growing-point. 
His descriptions and figures leave little doubt that the interpretation 
given by Barnes and Land applies to the whole of the Marchantiales— 
in all cases the chambers arise by splitting of cell-walls in originally 
compact tissue. In the simpler species of Riccia, this splitting 
occurs at a relatively late stage, and but little lateral expansion of 
the thallus occurs afterwards, hence the chambers form simply deep 
narrow vertical canals; but in Riccia fluitans, as in the majority of 
higher Marchantiales, the splitting stops short of the uppermost 
layer, and expansion occurs, so that the chambers become widened 
laterally ; finally, in Riccia natans, as in some of the higher forms 
(Operculatae and Bucegia), the splitting process is confined to 
certain portions at different depths from the surface, the result 
being a network of chambers forming a mass of spongy tissue. The 
writer has re-examined microtome preparations of various Marchan¬ 
tiales, and can confirm the accounts given by Barnes and Land and 
by Petsch, as to the schizogenous origin of the chambers, but 
cannot follow the former in referring each chamber in Marchantia, 
etc., to a single mother-cell. According to the diagram given by 
these authors, each chamber should, on their view, be separated 
from its neighbours by a double layer of cells ; but as a matter of 
fact these vertical partitions are usually only one cell in thickness. 
In the genus Riccia three types of air-chambers may be 
distinguished—(1) narrow canals bounded by four cell-rows, as in 
Riccia glanca, etc.; (2) wider canals bounded by about eight cell- 
rows, as in R. vesiculosa ; (3) wide chambers separated by lamellae, 
as in R. fluitans and the other species belonging to the section or 
sub-genus Ricciella. Juel (16) has shown that in R. Bischoffii the 
thicker median portion of the thallus shows air canals of the first 
(Euriccia) type, but in the thinner lateral wings of the thallus the 
chambers are wide and separated by lamellae, while between the 
“ midrib ” and the “ wings ” there are transitional chambers 
resembling those of R. vesiculosa. The differences between the 
three types are simply due to differences in rate and direction of 
growth of the tissues in the various regions of the thallus subsequent 
to the splitting by which the chambers are laid down in the first 
instance. The existence of transitions between the “ Euriccia ” 
and the “ Ricciella ” types makes it unnecessary to maintain the 
division of the genus Riccia into two or more sub-genera, which 
some writers have even raised to the rank of genera. 
Nicholson (27), in an admirable account of the Hepaticae of 
Sussex, records some interesting details concerning the morphology 
of various species of Riccia which he has observed in the field and 
cultivated indoors. His observations make it extremely probable 
