1907] 



BARNES &^ LAND— ORIGIN OF AIR CHAMBERS 



203 



4 



m 



points of the surface becoming overgrown by reason of the more rapid growth 

 of neighboring parts. There befalls these points quite the same fate as overtakes 

 the mother cells of the sex-organs, which at first indeed project above the sur£)ce, 

 but likewise become sunk in the tissue by being overgrown. The hollows in which 

 He the antheridia and archegonia (e. g., of Riccia) correspond completely in 

 their formation with the air chambers; and as both are laid down simultaneously, 

 they must attain an equal depth in the tissues; in other words the base of the sex- 

 organs lies at the same level as the inner boundary of the air chambers; and where 

 the sex-organs are aggregated in groups, they are surrounded for their whole 

 length by air chambers and are seated directly upon the compact tissue. 



There is no doubt as to Leitgeb's meaning, for he has both put 

 his declaration positively and denied categorically the other possible 

 modes of origin. Yet it is clear, both from his figures and from his 

 description, that he saw many clefts which can be most easily inter- 

 preted as due to spHtting; but apparently he did not in all cases see 

 the earliest stages of the air chambers, which can be interpreted in no 

 other way. It is not surprising, however, that so good an observer 

 missed them, as he had at his command almost none of the modern 

 technique. Rather it is surprising that he saw so much and so accu- 

 rately, for with the best technique it is not easy to discern the first 



F 



cleavage. 



A-priori reasoning, weak as it is, creates suspicion of the correct- 

 ness of Leitgeb^s view, and no figure of his shows any condition that 

 cannot be interpreted in consonance with schizogenous origin. It 

 is peculiarly difficult to conceive of a mode of growth such as he 

 describes, for nothing like it is known elsewhere. If the lowest point 

 of the pit is a point which originally 

 lay in the surface, and there is no 

 cleavage, then the progressive forma- 



fig 



the pit must be somewhat as in 

 In such a process the pit must 



ery 



Fig. I . 



Diagram of the 



would show a reentrant angle; indeed, ^^^^ ^; ^.; ^^^^^^^ ^^^,,^,g 



it is difficult to see why the pit would to Leitgeb. 



not be closed by turgor as fast as the 



adjacent cells grew up, unless one predicates rigidity at the base of 



the dome or a rapid growth at "the very surface in which the upgrowing 



cells did not share. When readv for the di\asions which are to pro- 



