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, 

 Lunnlaria, Conocephahim, Diimortiera, Aster ella (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 /. 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. 



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