1907] BARNES ^ LAND— ORIGIN OF AIR CHAMBERS 199 



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all as do the intercellular spaces of higher plants, by the cells separating, nor even 

 by progressive cleavage from outside inward; but they apjx^ar originally as 

 depressions in the surface, which arise by definite points (always situate wheTe 

 four cells meet) lagging in growth and so becoming overgrown by the adjacent 

 parts. 



While casually following the development of the spirelike air 

 chambers on the gamctophore of a species of Fimbriaria collected by 

 Dr. C, J. Chamberlain in ^lexico in 1904,^ our attention was attracted 

 to very young air chambers on a receptacle still very small. The 

 appearance of a cavity very close to the apical cell, and relatively 

 deep in the tissue, raised a doubt as to the possibility of its having 

 been overgrown so promptly by adjacent cells- On examining this 



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matter in the thallus, in longitudinal sections through the apical cell, 

 what we saw showed that a reinvestigation of the origin of the air 

 chambers was needed. 



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Accordingly, we' have examined as many of the Marchantiales 

 as have been easily obtainable. Although we have not studied all the 

 members of the group, but only representatives, the facts obsen'cd 

 are so uniform and unambiguous that it is unlikely there is any other 

 mode of origin than the one found in ever}' case examined. This 

 expectation derives force from the fact that our examination has 

 covered all types of air chamber, and that Leitgeb's extensive obser- 

 vations can be interpreted (as he himself confessed in regard to Mar- 

 chantia and Preissia) in consonance with schizogenous origin. 



Inasmuch as Leitgeb's view is accepted at present and we con- 

 sider it untenable, we quote some of his very unequivocal declarations, 

 to show that he has left no doubt as to his meaning. Speaking of 

 the Ricciaceae, after describing the quadratic surface mesh formed 

 by the walls of the cells near the growing point, he says:^ 



Soon one observes at the corners small pits, which arise thus: the growth of the 

 lateral w^alls of the outer cells, in so far as concerns the direction at right angles 



s Probably Fimbriaria echinella Gottsche. 



^ Bald bemerkt man an den Ecken kleine Griibchen welche dadurch entstehen, 

 dass das Wachsthum der Seitenwande der Aussenzellen, insoweit als es sich in der auf 

 der Dorsal flache senkrechten Richtung voUzieht, in den Kan ten geringer ist, als an den 

 iibrigen Stellen. Es entspricht daher der tiefste Punkt eines Griibchens dcm 

 (urspriinglich an der Oberflache gelegenen) anssersten Punkte der verkiirzt bleibenden 

 Seitenkante, und die das Griibchen umgrenzenden Wandstiicke sind Theile der 

 ursprunglichen Aussenwande, resp. aus diesen hervorgegangen. Indem nun dieser 



