k 



1907] 



BARNES ^ LAND— ORIGIN OF AIR CHAMBERS 



213 



general phenomenon, the formation of schizogenous intercellular 

 spaces. 



Our conclusions may be summarily staled thus: The air chambers 

 of Marchantiales arise invariably by the splitting of internal cell 

 walls, usually at the junction of the outermost and first internal 



» 



Fig. 22. — Plagiochasma sp.: o^ air chamber opening through pore; c, closed 



chamber. 



layer of cells. Thence, in one type splitting proceeds outwardly 

 and inwardly more extensively than laterally, and lateral enlargement 

 of the chamber folio w^s by growth; while in the other type expansion 

 of the chamber is due to extensive inward splitting accompanied by 

 growth. The origin of the air chamber is in all respects like that of 

 intercellular spaces in the vascular plants. 



The University of Chicago 



XoTE. — The figures arc all drawn to the same scale and appear here 

 magnified about 550 diameters. 



