segment is included the vein situated in 
its upper border anastomoses with the 
vein of the foregoing primary segment 
(fig. 446 A). The primary segment situated 
immediately over a branch may sometimes 
be included (fig. 452, segm. 9). The branch- 
es are as a rule regularly alternate, but 
superposed branches may occur (fig. 445). 1 
The mid-rib arising by tangential 
divisions, not only of the median cell but 
also of the adjacent parts of the primary 
segments, early attains a considerable thick- 
Kad EL, 
> = —<—— SE es 
nessandthelateral 
veins are also ear- 
ly developed, the 
cells in the up- 
lengthening and 
Fig. 449. 
Membranoptera alata. Portion however, not correct, they 
RP ONE EN re only oven off from the 
lateral veins and secondary 2 
pits. The limits of the primary lower side (fig. 446). Lateral 
segments are marked with an veins may also spring from 
arrow. 260 :1. 2 R x 
the mid-rib between the prim- 
ary lateral veins (fig. 446). The divisions parallel to 
the flat of the frond extend from the mid-rib towards 
the margin, so that the greater part of the frond 
consists of more than one layer of cells; the margin 
itself, however, is always monostromatic (fig. 448 B, C, 
comp. Kyrın 1923 p.111). The veins are rather close 
owing to the want of growth beyond the apical 
portion of the frond. 
Secondary pits are produced in great numbers 
and, in the membranaceous portion of the frond, 
in particular in the walls perpendicular to the longi- 
==— = 
Tann Vey DE 
HONOR 
u 
Fig. 448. 
per border of the Membranoptera alata. A, longitudinal section of young 
5 shoot. B, C, transverse sections of shoots. D, longitu- 
primary segments dinal section of lateral vein. 390: 1. 
dividing by walls parallel to the flat, in consequence of 
which the inner conducting cell becomes covered by a short- 
celled layer on both sides (fig. 448 D). Lateral veins of the second 
order are also early developed in the upper border of the seg- 
ments of the second order. According to Harvey (Phye. Brit. 
pl. 247 fig. 8) the lateral veins of the second order spring up- 
wards and downwards as well from the primary ones; this is, 
Fig. 450. 
Membranoptera alata, Adventitious shoots 
from an axil. 350: 1. 
