338 WILLIS ; MORPHOLOGY OF THE PODOSTEMACEÆ 
under water. What is the stimulus causing maturity in the 
flower has yet to he determined, whether greater exposure to 
light, more dissolved air in the water, reduced water-pressure, 
or other cause. The spathe (PI. XVII., figs. 2, 5) is adnate 
below to the pedicel, is long and narrow, and encloses the 
fiower until after fertilization. There is only one stamen, 
which stands closely up against the stigmas. Germination 
of the pollen takes place within the anther, but I have not 
been able to make out how the tubes pass to the stigmas. 
The ovary soon expands into the fruit after fertilization, 
and the spathe, which for a time lengthens with the pedicel, 
ultimately splits and falls away. 
The six main ribs of the ovary, but not the two dehiscence 
ribs, are provided with stout wings of delicate translucent 
tissue, a feature of specific distinction between this species 
and P. subulatus. PI. XVII., fig. 6, shows a cross section of 
the ovary, and fig. 9 of the resulting fruit. These show, as 
has already been partly described under P. subulatus, the 
way in which the ribs of the fruit are formed. In cross 
section the ovary shows a stout placenta, two thin septa, 
and six wings, each with a vascular bundle. There are also 
vascular bundles in the place where the dehiscence ribs are 
to form. The inner epidermis in section shows a bright 
yellow colour ; it consists (fig. 8) of long narrow cells with 
very stout outer cutinized walls. Under it is a layer of 
smaller somewhat thick- walled cells, and beneath this again, 
towards the outer side of the ovary, is large-celled 
parenchyma tissue. As the fruit ripens, this parenchyma 
falls away, and the vascular bundles and the inner epidermis 
and layer of cells under it alone persist. The inner layer of 
cells and the outer parts of the bundles become lignified, 
while the inner epidermis forms a smooth shiny inner layer 
to the fruit wall. By the fall of the parenchymatous wings, 
the two dehiscence ribs become almost as prominent as the 
other six, and the two sides of each bundle become woody, 
but not the central line, in which dehiscence takes place. 
As seen in fig. 7 the stout inner epidermis also ends on either 
