Flower And Fruit 173

the pollen is ready for use. The different stages in the
opening of this flower are most peculiar, but, so far
as can be learned, have no direct bearing on its pollin-
ation. First the perianth tube opens at the tip to
expose the apex of the style, where the stigma, lying
in a small depresssion, is not yet ready to receive the
pollen. Next, longitudinal splits appear near the base
of the tube, and finally the whole perianth splits into
four segments which curl back. Thus the inflorescence,
which bears a considerable number of flowers, forms,
when mature, a tangled mass of perianth lobes. The
tuis, thrusting their tongues among the now exposed
styles, get the pollen dusted on their heads, and may
carry it to other flowers in which the stigma has
arrived at the receptive stage. In this way cross-
pollination is effected.

Water is, in some rare instances, the agent of pollin-
ation. This is the case with vallisneria (Fig. 110), the
male plant of which is so plentiful in Lake Takapuna,
where, beginning as a tiny shoot, it has vegetatively
reproduced till it is a serious impediment to the use
of boats upon the lake. The plant is dioceous The
stem having the pistillate flower rises to the surfce
where the flower opens and displays its stigmas. The
staminate flower, however, is produced below the water
at the end of a short stalk. Before the buds expand
they break off and rise to the surface, where they
open and expose their staments. These, floating on the
surface, may come into contact with pistillate flowers
and thus bring about cross-pollination, which, of course,
seeing that the plant is dioecious, is the only kind
possible.