ENA LUS ACOROIDES. 
277 
parietal placentas project to the middle of the ovary and are, 
as in so many of the Hydrocharitaceæ (cf. Eichler, 8), split 
quite into two lamellae. During an early stage there are rather 
Fig- g. —Transverse section of a fruit with embryos. Nearly all 
mucilage gone and the air-chambers pressed together (lft x 1). 
large air-chambersbetween these, but when the embryos grow 
out they disappear as the lamellae become pressed together 
(fig. 6). It is the low specific gravity due to these and also 
some other air-chambers in the ovary that keeps the flower 
floating before the pollination. Afterwards when the fruit 
is drawn down by the spiral rolling up of the pedicel, the 
air-chambers between the split placentae disappear. 
8(10)04 (19) 
