Black. — The Morphology of Ricci a Frostii , Aust . 513 
at the apex of the thallus. Like Riccia crystalling Leitgeb (1. c., p. 13 ), the 
segments on the ventral side are limited and do not form ventral scales or 
lamellae, as they do in R.glauca (Campbell, 1. c., p. 25 ). Fig. 6 represents 
a longitudinal vertical section cut through the growing point. It ends in 
a large wedge-shaped apical cell, from which cell-rows are cut off. On the 
dorsal side, segments are cut off which eventually become the upright 
filaments. A transverse section cut through the growing end of a thallus 
(Fig. 7 ) illustrates the dichotomous branching. The cell-rows cut off on 
either side arch over the growing point and are in an inclined or an almost 
horizontal position. In older parts of the thallus these cell-rows are erect. 
The growing points are distinguished by their dense contents and large 
nuclei. 
Recent investigations of the air-chambers of the Marchantiales have 
brought into question the account of Leitgeb, who attributes the air-chamber 
and the sex-organ pit to the same origin in the Ricciaceae. His summary 
of the formation of the air-chambers and the stomata states that the origin 
of the air-spaces is caused by the growth of cells surrounding a depression 
which first appears on the surface. The continued upward growth of these 
cells forms the air-space, and the origin, therefore, is not due to a splitting 
from the outside inward, nor to a separation of cells. Goebel (23) states 
that the air cavities in the Riccieae do not arise schizogenetically like the 
intercellular spaces of higher plants, but in a manner as shown by Leitgeb, 
beginning in a depression at the junction of four cells, and originating as 
a natural consequence of the upward growth of the adjacent cells. Barnes 
and Land (4) studied the origin and nature of the air-chambers in the 
following forms : Fimbriaria , Marchantia , Lnnularia , Conocephalus , Dumor- 
iiera , Plagiochasma , and Ricciocarpus nata7is and Riccia jluitans, and con- 
cluded that ‘ the air-chambers of the Marchantiales arise invariably by the 
splitting of internal cell-walls usually at the junction of the outermost and 
first internal layer of cells. Thence, in one type, splitting proceeds out- 
wardly and inwardly more extensively than laterally, and lateral enlarge- 
ment of the chamber follows by growth ; while in the other type expansion 
of the chamber is due to extensive inward splitting accompanied by growth. 
The origin of the air-chamber is in all respects like that of the intercellular 
spaces in the vascular plants.’ It is significant that Barnes and Land 
described only two forms of the Ricciaceae, and the two examined had the 
character of air-chamber of the other forms described by them. 
Miss Hirsh (24), in a study of the air-chambers in the Ricciaceae based 
primarily upon Riccia Frostii , included the examination of fresh material 
of Ricciocarpus natans and herbarium material of Riccia nigrella, R.glauca , 
R. Miyake ana , R. crystallina , R. arvensis hirta , R.fluitans , and R. DonnelliL 
Her examination of Ricciocarpus natans confirms the statement of Barnes 
and Land that the air-spaces in this plant arise through internal cleavage 
