BN ALUS ACOROIDES. 
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CJymodocea, and Halophila, where the pollen is vermiform. 
But the epihydrogamics also represent many different 
methods of pollination. I have already shown above that 
Enalus does not agree so completely with Yallisneria in this 
respect as was perhaps previously supposed. But it may 
also be of some interest to make a further comparison with 
some other hydrophilous plants. 
A careful examination of Elodea canadensis has recently 
been made by Wylie (35). As regards the female flower it is 
of interest to see that in Elodea also its floating upon the 
surface is due to the buoyancy of the gases in large lacunae, 
which here arise in the long floral tube according to Wylie 
(35), but in the elongated part of the ovary according to 
Raunkiaer (22, p. 135, fig. 63). In Enalus the lacunae are 
formed by the split placentae (fig. 5). The organization of 
Elodea otherwise reminds one more of the female flower of 
Yallisneria than of Enalus ; the perianth, however, is double, 
but the flower floats with the axis vertical, the weight of the 
flower resting chiefly upon the stigmas (Wylie). The pollen 
grains of Elodea are very remarkable. The male flowers 
develop just as in Yallisneria and Enalus; they loosen at 
maturity and rise to the surface in the same manner. 
It is interesting to note that Wylie has observed a periodi¬ 
city in the detachment of the male flowers in Elodea also. 
They are chiefly raised to the surface during the early part 
of the forenoon, and very few in the evening. This 
phenomenon, Wylie suggests, may be due to the first 
photosynthesis of the day. The oxygen hereby accumulated 
makes the flowers which have ripened during the hours of 
darkness float up. I have made no observations on the 
influence of the light upon the male flowers of Enalus and 
their detachment, but, as I have already mentioned above, 
the male flowers of Enalus almost without exception float 
up only during low water, which I think is due to the 
pressure of the water. But Elodea is never exposed to any 
such changes, as it lives in lakes and rivers. 
