1894.] Flistology of the Pontederiacee. I8I 
The cross-partitions, or diaphragms, are horizontal or ob- 
lique and are composed of polygonal cells, with interstitial 
air-spaces at the angles leading from one chamber to another. 
The cell walls in some of the partitions are very thick. Ac- 
cording to De Bary’ ‘‘air-passages in internodes, petioles, 
and leaves of most monocots are partitioned by diaphragms,” 
or “'stellate tissue,” as it is frequently called. De Bary fur- 
thermore makes the general statement that Pontederia has 
diaphragms composed of many-armed cells ‘forming a plate 
with wide lacunz.” In the plates of P. crassipes, ‘‘intersti- 
tial spaces” is the more correct term for the openings between 
the cells, because they are of much smaller volume than the 
Surrounding cells. True lacunar cavities occur in the dia- 
phragms of P. cordata, however, while those of Heteranthera 
limosa and H. reniformis are small like those of P. crassipes. 
The cells of the diaphragm each have well-defined nuclei and 
granular protoplasmic contents, with a few starch grains. 
These diaphragms Probably serve several purposes. Duval 
Jouve Suggests that besides the function of allowing the pas- 
‘age of air, they have the office of support points for the 
0ss-running® fibrovascular bundles. No transverse bun- 
dles, however, were noticed in P. crassipes, while in P. cor- 
few of the cross-plates of the smaller peri- 
do they occur, those of the central cavity be- 
ightness is secured. A large air-passage usually 
ep upanies each bundle, traversing the leaf side by side 
Stomates are abundant on both sides of the 
petioles of all the species except Heteran- 
faminea, the latter being submerged. The epidermal 
those és om are somewhat thin-walled with the exception of 
Outer walls, sy 
The Closed y 
Species, 
ata, which have minute tubercles on their 
ascular bundles are very similar in all the 
©y are surrounded usually by one layer of par- 
ew scl th a large amount of bast in the phloém and 
e 
Fenchyma cells opposite. Mr. Wilcox says that 
Rene. Anat., 217 
In Bot. Jahres, Tr 196. 
