X J 



212 



BOTANICAL GAZETTE 



[SEPTEMBER 



formation of the aerating system is mainly due to splitting and 



growth. 



How Leitgeb discounted the evidence of his eyes is well show^n 



in the case of Plagiochasma, 

 in which he saw and figured 

 intercellular spaces/^ as to 

 which he remarks :^^ 



In P. Aiionia they (the air 

 chambers) appear in both longi- 

 tudinal and cross- sections very 

 commonly in the form of extremely 

 small intercellular spaces, like 

 those in ordinary parenchyma, 

 and one could scarcely dismiss the 

 idea that they are formed by cleav- 

 age in originally compact tissue^ did 

 not corresponding relations in other 

 species speak against this interpre- 

 tation. 



Fig. 20. — Plagiochasma sp. Beginning 

 of pore margin. 



As a matter of fact, corresponding relations in other species do not 



speak 



against 



this 



in 



terpretation^ but con- 

 firm it, 



Finally we may point 

 out that, instead of homol- 

 ogizing the formation of 

 the air chambers in 

 Marchantiales with the 

 formation of 



sex-organ 



pits, which it required 

 considerable distortion of 

 the facts to do, we have 

 brought their origin into 

 line with the much more 



Fig. 



complete. 



21 



Plagiochasma sp. Pore margin 



Lebemioose 



Form ausserst kleiner Intercellularraume, wie sie im gewohnlichen 



Annahme 



haufig 



lichem fest gefugtem Gewebe. kaum von der Hand weissen, wenn nicht die entsprech- 

 enden Verhaltnisse bei den iibrigen Arten gegen diese Deutung sprechen wiirden.- - 



/. c, p. 64. 



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