1907] 



BARNES &^ LAND— ORIGIN OF AIR CHAMBERS 



211 



I 



but the passages are always deep and narrow, with hardly more than 

 the pore margin for a roof (fig. 21), There are many spaces near the 



Fig. 18. — Plagiochasma sp.: a, apical cell; r-5, air chambers; 4a secondary 

 splitting between primarj' clefts 4^ 5. 



surface which have no direct opening by pore {fig. 22 ^ c). These 

 connect doubtless with the spaces that do have pores {fig. 22 ^ 0). 

 Whether partitioning of the chambers occurs, as described by Leitgeb, 



Fig. 19, — Plagiochasma sp.: a, apical cell; 1-4, air chambers; ja, secondary 



splitting 



by the outgrowth of cell plates in Plagiochasma and in Ricciocarpus, 

 we have not fully determined, though it appears probable; but the 



