Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS 243 
According to Barnes and Land there is nothing to support 
Leitgeb’s views. In their opinion the chambers always originate 
in compact tissue below the surface of the young thallus by a 
splitting of cell-walls and, in case the mature chamber has an 
epidermal pore, the splitting extends upward until the surface is 
reached. They based their conclusions on a study of Ricciella 
(Riccia fluitans L.), Ricciocarpus (Riccia natans L.), Marchantia, 
Lunularia, Conocephalum, Dumortiera, Asterella (Fimbriaria), 
and Plagiochasma, and assumed that they would apply as well to 
Riccia (in its restricted sense). After the chambers are once 
established their increase in size need not involve any further 
schizogenous processes. It is largely brought about by the growth 
of the cells surrounding the chamber, and may be wholly brought 
about in this way; in other words, by the surface extension of the 
bounding cell-walls. According to Leitgeb’s ideas the increase in 
the size of the chambers is brought about in much the same way, 
except that a total absence of splitting is always assumed. It 
will be seen, therefore, that the most important differences between - 
the two explanations are concerned with the very beginning of the 
developmental process: according to Leitgeb the chamber is 
superficial in origin and no splitting occurs; according to Barnes 
and Land the chamber is not superficial in origin and splitting does 
occur. 
Among recent papers dealing with air chambers, those by 
Miss Hirsh (4), Pietsch (8), Deutsch (3), Miss O’Keeffe (7) and 
Miss Black (2) may be briefly noted. Miss Hirsh’s work is based 
largely on Ricciocarpus natans (L.) Corda and Riccia Frostii Aust. 
She reaches the conclusion that the first of these species agrees 
with Barnes and Land’s explanation, while the second agrees with 
Leitgeb’s. Her figures of R. Frostii, however, by no means support 
this conclusion fully. Although they show that the chambers 
drawn may have been superficial in origin, they show as well that a 
splitting must sometimes have occurred, because some of the cham- 
bers extend below the original surface of the thallus. This is 
brought out clearly by her f. 6, upon which she lays especial 
emphasis. This figure, in fact, presents no convincing evidence 
that the chamber may not have been initiated by a schizogenous 
process. 
