10. 

 till late in tlio development ol' the lunina (Figs. u4, ol). 

 The next v.'all fonnecl after v/all V is toward tlie ventral 

 side of the marginal cell ( VI , Figs. 34, 35 ), contin- 

 uing tlius t]Le regular alternation of the section v/all s. 

 Tlien vrall VII is formed toward the dorsal side of the 

 cell, \7all VIII toward the ventr:.;.l side, and so on till 

 a large number of sections, if we may still call hem such, 

 have "been fonned (Fig# 35), the marginal cell "being still 

 distinguishable, and pro'bably active, v/hen the pinnae are 

 more than tv/o millimeters broad. Th.ese additional sections 

 divide like the earlier ones by periclines to foi-m the 

 plerome, periblem and dermatogen la.yers and later by 3Jiti- 

 clines (Fig. 35), fonning thus the various tissues of the 

 leunina. Meanv/hile the marginal cells divide also by anti- 

 clines perpendicular to the edge of tlie pinna (Fig. 33), 

 Tliey tlius constcintly increase in number and foi^m a rounded 

 growing edge, as Hanstein (*G5) has shov/n, the pinna fi- 

 nally becoming v;edge shaped with a broad rounded outer end, 



in the matm^e leaf. The pinnae are directed more ven- 

 trally than laterally from the petiole even at the begin- 

 ning, £U"!d those of the upper or younger pair soon come 

 to liave trieir ventral surfaces nearly in contact, wliile 

 tlie lo'.ver imd older pair are folded togetlier in the leaf 

 bud so as to enclose tlie younger ones between them (Fir.SC). 



