i 



2IO 



BOTANICAL GAZETTE 



• 



[SEPTEMBICR 



means all of the tissues arising from the dorsal segments of the apical 



cell show splitting, but much the greater part is compact, with no inter- 

 cellular spaces of 



any 



kind, 



In 



Fimbriaria and 

 Plagiochasma, 

 however, the 

 splitting involves 



all 



the tissue 



w 



hich 



arises 



Fig. i6. — Fimbriaria echinella: a, apical cell; b-e, succes- 

 sive segments; z, 2, air chambers; in d cl secondary deep- 

 seated cleft. 



from the dorsal 

 segments of the 

 apical cell, so 



that 



a 



much 



greater part of 

 the thallus is permeated by extensive and irregular air passages (fig. 

 i6), which make it almost as spongy as Ricciocarpus. 



In Fimbriaria the primary splitting usually begins between the 



cells arising from successive segments (fig. i6y ^' ^5 where lies 

 between segments c and d, and ^ between d and e). Later, and often 

 deep in the tissue, secondary splitting gives rise to intercellular spaces 

 which may reach the surface or may break into a primary space. 



In Plagiochasma the splitting is likewise more pronounced between 

 the offspring of different segments (fig, iy)y but the secondar)^ splitting 

 if such it may be 

 called, occurs so 

 promptly and be- 

 comes so extensive 

 as to be hardly dis- 



j 



tinguishable 



from 



the primary {figs. 18 y 



^9. 



F 



air 



3a, 4a 



). 



passages 



The 

 are 



open almost or quite air chambers. 



uninterruptedly until 



the pore margin is well begun {fig 



Fig. 17, — Plagiochasma sp : a, apical cell; ^"3 



There is never a wide and 

 'ea a roof forms, pari passu; 





I 



