/ • 



pleromo of sections III :jia IV uiviuu v.y like the 

 plorome of section I , "by frequent periclines imd Icnf^i- 

 tudinal tinticlines, and by fev/or trcinsverce anticlines, 

 to form with this the remaining tissues of the axial bundle. 

 Tlie small cells of the outer layer of the bimdle gradually 

 become more regular in shape and unifoi-ro in size, forming 

 thus the characteristic bundle sheath (b,s..Figs. 18, 19). 



Tlie plerome of the ultimate marginalcell never takes 

 any part in the formation of the s^.ial bundle, but in some 

 cases that of section V apparently contributes to the 

 fonaation of tlie sheatli and of a fev/ cells within this 

 (Fig. 13). 



Tlie Lamina. 



By the time tliat the apical cell of the leaf has 

 ceased to cut off segments, the tenth and eleventh (or e- 

 leventh and twelfth) segments from the base on each side, 

 have begun to grow out laterally and ventral ly to form the 

 first pair of pinnae (p!. Fig, c-l). Tlicso pinnaa do no- 

 co^^ospond in oxt.an". oxac'/iy with the s^gmrai , l'.s 

 h-nn shov.Ti to do in Asplenium serpent ini by Sadebeck ('7?) 

 and in Onoclea struthioptoris by Campbell ('87). In tliis 

 respect they agree rather v/itli the pinnae of Ceratopteris 

 thalictroides, as described by Kjiy ('?"). The lower border 



