284 SVEDEIiITTS : IiIFE-HISTORY OF 
phenomenon may be the following. With increased pressure, 
during high water, the buds are somewhat compressed, 
and consequently the volume diminishes, but since their 
absolute weight is the same it follows that the specific gravity 
is increased and consequently the power of attraction up¬ 
wards diminished. With diminished pressure again, during 
low water, the volume of the buds is augmented and thus 
the specific gravity diminished, so that the power of attraction 
upwards is augmented. The chance for the male flowers to 
rise to the surface during low water is consequently greater 
than during high water, in otherwise similar circumstances. 
Thus there is in this plant a remarkable correlation 
between the exposition of the female flowers and the loosening 
of the male flowers , in that both these phenomena always 
occur at the same time , during low water. 
For the full comprehension of the significance of this fact 
the occurrence and geographical distribution of Enalus may 
be of some interest. The difference in the rise and the fall 
of the tide in Ceylon is rather small, about \ m. or more, but 
great enough to keep the Enalus flower submerged during 
high water. But this plant occurs in other parts of the world 
where the difference in the tide levels is very great. Thus 
Balansa notes (sec. Sauvageau 28, p. 269) that Enalus 
acoroides in New Caledonia grows in a depth of (at high 
water) 2-3 m. and Volkens (36, p. 455) states that in the 
Caroline Islands it is 1-2 m. below the surface level at 
high water. As Enalus never reaches more than about 1 m * 
in height, it is evident that in these parts of the world the 
female flowers of this plant never have any chance to reach 
the surface except during low water. 
As may be seen from this description, there are somewhat 
essential differences between Enalus and Vallisneria in the 
mode of pollination, and these are closely connected with the 
different morphological organization of the’flowers. 
One may compare, for instance, Keraer’s description ^ ’ 
p. 129) of the pollination of Vallisneria. As regards the 
