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Scientific Memoirs by
corolla. Up to this time, too, the calyx is closed, the three sepals composing it
adhering to one another marginally, so that the cavity of the flower is completely
separated from the surrounding water by two continuous coverings—one bracteal
and one calycine. During the course of the night, previous to blowing, the apex
of the bracteal sheath gives way under the pressure of the included and growing
flower, and the tip of the bud then protrudes free into the water. Development
now advances rapidly. In the early morning the buds are still quite closed, the
sepals still being closely applied to one another and completely concealing the white
petals from view. If the plant in this condition be well exposed to the access of
sunshine, active discharge of large bubbles from the interior of the bud now sets in,
the rate of evolution varying under various circumstances—the degree of exposure
to light, the general vigour of the plant, &c. (vide Note A). If a closed bud in
an active state of gaseous evolution be examined, it will be found that the essential
organs have already matured, that an abundance of pollen is smeared on the stigmas
and on the interior of the corolla at the level of the fully open anthers, and that
free germination of pollen grains and passage of pollen tubes down the greater part
of the length of the central stylar canals has already taken place (Plate VI, Fig. 4).
Gradual opening of the calyx and protrusion of the folded petals soon occur,
these processes being aided by the continuous accumulation of gas within the
cavity of the flower and its intermittent discharge in the form of large bubbles
passing out between the opposed margins of the sepals and petals. Unfolding of the
corolla next occurs, active evolution of gas continuing as before. When once, how-
ever, the corolla is fully unfolded, the surrounding water descends into its cavity
and appears to come into direct contact with the stigmas and styles. In the
course of the afternoon active evolution of gas gradually diminishes, and with
sunset comes to a close. The flower is at this time fully expanded and the corolla
retains its pure white colour, the water apparently hardly coming into contact with
it, especially externally, owing to the thick stratum of adherent bubbles of
gas with which it is coated. On the following morning this gaseous coating is
absent, the corolla is already brownish and macerated, and no further evolu-
tion of gas from the flower takes place on the renewed incidence of sunlight.
In studying these phenomena, one of the first questions which naturally
suggests itself is whether the gas discharged by the flower is of the same quality
as that evolved from the plant generally, or whether it is the product of special res-
piratory processes connected with the maturation of the floral organs and the occur-
rence of fertilisation. The large quantities of gas which are discharged permit of
the ready determination of this point, and the analysis of the gases collected from
the flowers and the rest of the plant separately show that the quality is in both cases
alike. In both cases there is an absence of carbonic acid, and the gas consists of
a mixture of atmospheric air and oxygen. The proportions of atmospheric air and
oxygen in 100 volumes of the gas in one experiment where this point was specially
determined were 62.42 atmospheric air to 37.58 oxygen. The next question calling