374 WILLIS : MORPHOLOGY OP THE PODOSTEMACBÆ 
The flower opens as soon as exposed to the air, and thus, 
owing to the erectness of the secondary shoots, has generally 
ripened its fruit by the time the whole plant is exposed 
upon the dry rock. It is figured in PL XXX., fig. 4, and has 
the usual structure of the flowers of this group of Podoste- 
inaceæ, with stamens slightly exceeding the stigmas. It is 
anemophilous, and apparently largely self-fertilized. It is 
quite sessile among the upper leaves of the shoot. It ripens 
quickly into a comparatively large smooth fruit, which has 
a broad dehiscence rib only very faintly prominent on either 
side, and a stouter rib in the centre of each valve (fig. 5). 
One valve remains persistent on the stalk after dehiscence, 
while the smaller and the seeds fall away. The persistent 
valve often curves inwards as in fig. 6 in dry air. The wall 
of the fruit (fig. 7) shows a very similar structure to that of 
Griffithella, with stout sclerenchyma layers. The ripe fruit 
has a smooth exterior, from which the parenchymatous 
outer layers of the ovary wall have fallen away. It very 
commonly stands on a long or short pedicel, owing to the 
falling away of the upper leaves and the cortex of the stem. 
The upper part of the pedicel is usually bifid, consisting of 
the two vascular strands that formerly went to the ovary, 
with their woody sheaths. 
Rejuvenescence . — I have not observed any evidence of the 
occurrence of this phenomenon, but in all probability it 
occurs as usual. 
Comparing Willisia with preceding genera, it is evident 
that in some respects it is more on the level of Podostemon, 
in that it has large and complex secondary shoots. On the 
other hand, these bear each only one flower. The flowering 
takes place while the water is still comparatively deep, 
though the seeds are ultimately shed upon the rocks. In one 
species of Podostemon we had an indication of a crustaceous 
type of thallus, which, however, was more of the Dicræa 
type ; in Willisia we get a crustaceous closely attached 
