5 H Black . — The Morphology of Riccia Frostii , Aust. 
and have no relation with the sex-organ pit, but in four of the other forms 
examined, R. nigrella , R. glauca , R. Miyake ana, and R. Frostii, a different 
type of air-chamber was found from that of Ricciocarpus natans and 
R. fluitans. Miss Hirsh, in describing the origin of the air-spaces in Riccia 
Frostii , Aust., says ( 1 . c. } p. 203), ‘ Immediately back of the apical cell the 
superficial cells arch outward in a papillate manner, as a result of the 
cessation of growth at the lines of their junction. As they elongate they 
are divided by transverse walls, so that filaments or rows of cells are formed, 
which are separate and distinct from one another. The intervening spaces 
in this species are formed, therefore, not by the cleavage or the separation 
of mature tissues, but in a manner exactly indicated by the diagrammatic 
scheme given by Barnes and Land in their Fig. 1.’ Miss Hirsh concludes 
that there are two methods of the origin of the air-spaces in the Ricciaceae : 
one, by internal cleavage resulting in irregular air-spaces separated by 
plates of cells one layer thick, as in Ricciocarpus natans ; the other by the 
upward growth of filaments at right angles to the surface of the thallus, 
forming narrow chambers or canals, as in Riccia Frostii , Aust. It will be 
seen that Miss Hirsh supports the theory of Leitgeb, and her work is also 
in harmony with the description given by Campbell ( 1 . c., p. 25). The 
writer’s observations of Riccia Frostii are in agreement with those of 
Miss Hirsh. 
Fig. 6 is a stage similar to Figs. 4, 5, and 6 of Miss Hirsh. The apical 
cell is seen at the apex, and back of this are depressions which become the 
air-spaces by the upward growth of the adjacent cells. The cell-row is seen 
to have become more than one cell thick in certain cells, initiating the 
widening of the air-spaces. The transverse section (Fig. 7) shows almost 
the same condition as the longitudinal in the papillate surface of the growing 
point, and at either side are the cell-rows with the canal-like air-spaces 
between them. The fully developed air-chamber is a canal of irregular 
polygonal shape, separated by plates of chlorophyll-bearing tissue, one cell 
in thickness, as seen in Fig. 8, a section cut parallel to the surface in 
a mature thallus. The number of cells bounding an air-space may therefore 
vary considerably in different parts of the thallus. This has been 
pointed out by Juel ( 28 ) in an article 1 on Riccia Bischoffii . The small 
depressions or pits on the surface of the thallus are the openings of the air- 
spaces which lead in an indefinite manner to the surface cells. The thallus 
of R. Frostii is similar to that of R. glauca described by Campbell ( 1 . c., p. 28), 
and consists of the ventral part, a compact tissue with no air-spaces, from 
which the rhizoids spring. From this compact tissue the upright filaments 
arise, forming the elongated air-chambers. The terminal cells of the 
filaments are somewhat swollen and have scanty contents. Goebel ( 1 . c., p. 72) 
refers to the lack of chlorophyll in the outermost layer of cells, and considers 
1 From current literature in the Bot. Gaz., li, p. 479, 1911. 
