244 Evans: Air chambers of Grimaldia fragrans 



Pietsch's work is remarkable for its thoroughness and accuracy. 

 It deals with species of Riccia and Ricciella, and his account is 

 therefore' based on the group of plants from which Leitgeb drew 

 his conclusions. Although he criticises the work done by Barnes 

 and Land, his observations lead to similar conclusions, so far as 

 the development of the air chambers is concerned. He finds that 

 even in Riccia the chambers originate from a splitting of cell walls, 

 the split beginning below the surface and then extending upward 

 until the surface is reached. 



Deutsch's paper, devoted to Targionia hypophylla L., includes 

 an interesting observation on the development of the air chambers. 

 He states that they arise by a splitting apart of cells close to the 

 apical cell but maintains that the split begins on the outside and 

 extends inward, instead of beginning below the surface and extend- 

 ing outward. The/, j, which he cites as evidence, would be more 

 convincing if the youngest chamber shown did not extend into 

 the hypodermal tissues; as the figure stands it might equally well 

 bear the opposite interpretation from the one drawn. Deutsch 

 does not consider that his account differs in any essential respect 

 from the explanation of Barnes and Land, in spite of the super- 

 ficial origin which he assigns to the chambers. Miss O'Keeffe, 

 who also worked on Targionia, fully supports Deutsch in his 

 statements about the origin of the chambers. Fortunately, the 

 youngest chamber which she shows (f. i, A, a) seems to be con- 

 clusive; it appears in longitudinal section as a split between two 

 superficial cells and does not extend beyond them. 



Miss Black's paper deals with Riccia Frostii, one of the species 

 investigated by Miss Hirsh, and the same conclusions are drawn 

 as to the origin of the air chambers. Her/. 6, however, is open to 

 the same criticism as Miss Hirsh's figures. It represents the 

 apical region of a thallus cut longitudinally and including live 

 young air chambers, but even the youngest of these projects below 

 the original surface, showing that a splitting of a cell wall must 

 have taken place. Miss Black emphasizes the fact that she ob- 

 served no cases in which an intercellular space appeared below the 

 surface and then broke through to the outside, so that her con- 

 clusion regarding the superficial origin of the chambers seems 

 justified. At the same time her figure presents no evidence that 



