404 BOTANICAL GAZETTE [DECEMBER 
dividing by several successive periclinal walls, as most of the segments 
promptly do, the superficial parts remain for some time conspicu- 
ously undivided (, ~’, fig. 1), and so are distinguishable by their 
depth. In particular it is the final periclinal divisions that fail. 
This will be more evident by following the usual segmentation of 
the mother cell of an air chamber. In fig. 2, the young air chamber / 
originated as usual in a cell which underwent one periclinal division, 
es 
KSes é 
Fic. 5.—Elongation of a single gem- Fic. 6.—A somewhat later stage than 
miparous cell (p); w, rim cells, the fig. 5. 
posterior oldest and most advanced in 
division, 
forming the wall x, r; then an anticlinal one (2, 2); these two — 
cells each divided periclinally ( 3, 3), and cleavage occurred at the 
Junction of walls 2 and 3. (The curved anticlinal walls, 4 + aa 
ceeded the cleavage.) It is the divisions z, 1, and 3, 3, ri 
latter, which do not appear in the gemmiparous areas (P, P’) 
The relative extent of the area which these undivided ¢ 
and the occurrence of somewhat different cells Go} bee” are 
make it not unlikely that in figs. 1 and 2 the primordia of two pet 
are laid down in close succession; but of this we cannot be sure 
The failure of the gemmiparous cells to divide allows their neigh 
ells covel, 
