274 SVBDELIUS: LIFE-HISTORY OF 
fibrous layer is not developed (fig. 4), just as in so many 
other water plants. The anthers are clothed on the outside 
with rather large papillae (PI. XXIV., A, fig. 6) which are 
supplied with a series of delicate reticular folds. 
The pollen grains (PI. XXIV., A, fig. 21) are very large: 
they average about 170-175/* in diameter, consequently 
Enalus in this respect belongs to that group of plants which 
have the largest known pollen ( cf Kerner 16, p. 96). The 
pollen grains contain besides drops of oil a large number of 
finely distributed starch grains ; they are thus very heavy 
and sink in sea-water. Thus they behave like the pollen 
grains of Nqjas, examined and described by Jonsson (15). 
Also, as in so many other water plants, e.g., Ruppia 
(Murbeck, 20), Zannichellia, Najas (Jonsson, 15), and 
Ceratophyllum (Strasburger, 32) the pollen grains of 
Enalus have no intine, and are quite smooth on the surface 
(PI. XXIV., A, fig. 21). 
The number of the pollen grains seems always to be in a 
certain correlation to their size {cf. Kerner, Pflanzenleben, 
II., p. 94). But in Enalus there are so many male flowers 
developed—a whole male inflorescence is homologous with 
a single female flower—that the diminished chance of 
securing pollination, which a smaller number of developed 
pollen grains must otherwise cause, is neutralized. 
The Female Flower .—The spathe-leaves of the female flower 
when fully developed (PI. XXIV., A, fig. 8) are rather 
different in shape from those of the male inflorescence. 
These differences are closely dependent on the arrangements 
for the pollination of the flower. At an earlier stage (PI- 
XXIV., A, fig. 7) they agree more with the male spathe-leaves 
as to their form and the position of the leaves, but in regard 
to the size there is a difference, as they.are much narrower, 
so that the breadth of the whole bud would not much exceed 
10 mm., and during the whole anthesis the spathe maintains 
this breadth at the base. After the pollination, during the 
increase of the fruit, the spathe-leaves are pressed m° re 
