42 Scientific Memoirs by
The germinating tubes push their way inwards through the hairy tissue of
the edges of the stigmas, to reach their smooth central surfaces, and then pass
vertically down these and the stylar canal which is continuous with them. The
number of pollen grains which have germinated in situ within the anther lobes is
sometimes so great as to cause the anthers to adhere to the stigmas, and the
mass of tubes traversing the stylar canal is so great as to form a thread readily
distinguishable by the unaided eye if the style be carefully divided and the distal
and proximal portions gently separated from one another (vide Note D).
All these processes of maturation of anthers and stigmas, germination of
pollen grains, and ingrowth of pollen tubes, take place ere the flower-bud has ex-
panded, and at a time when in submerged specimens its cavity is constantly
occupied by gas distending the floral chamber and discharging its excess in
the form of a continuous stream of bubbles, which force their way out between the
margins of the floral envelopes.
The evolution of gas seems to take place from all parts of the flower, but
mainly from the internal surfaces of the sepals, the external surface of the petals,
and the tissue of the upper extremity of the centre of the ovary at the bases of
the styles and continuous with the very open tissue which holds the central ex-
tremities of the ovarian follicles in relation to one another. When the petals
of an unexpanded flower are gently removed, the constant accumulation of gas
under the influence of sunlight within the floral cavity can be very clearly ob-
served. As the mass of gas increases, the sepals are gradually more and more
separated from one another, the gas gradually protrudes more and more between
their lateral edges or tips, and, when the tension has risen beyond a certain pitch,
is partially discharged in the form of bubbles, with proportionate collapse of the
calycine cavity. Similar phenomena appear when the petals are retained and
the sepals removed. Pulsatory distension of the floral cavity and emission of
bubbles here also manifests itself, although not with such intensity as in the pre-
vious case. Where both sepals and petals are removed a continuous discharge
of small bubbles from between the bases of the styles and filaments becomes
evident. As previously mentioned, after the corolla has expanded, which only
happens after the occurrence of fertilisation, the amount of gaseous evolution
rapidly diminishes, and little further discharge appears to occur, save for a time,
from the external surfaces of the petals, which are usually thickly coated with large
adherent bubbles, and the water now descends freely into the cavity of the flower.
Taking all these facts into account, there can, I think, be no doubt that the
excessive gaseous evolution taking place from the flowers of Ottelia during the
earlier part of their period of maturation has arisen in connection with the exter-
nal conditions to which the majority of the flowers are exposed, and serves the end
of securing the fertilisation of the flowers of the most vigorous plants by pre-
venting the access of water to their essential reproductive apparatus until the
processes of fertilisation have been effectually carried out.