However, the story must be completed because arrival of pollen grains at the micropyle is the beginning of more complex processes, as first pointed out by Joseph Doyle (1945).
The only suggested explanation for the functional significance of this peculiar phenomenon is by Takaso and Owens (2008) who suggest that the exine-less grain is flexible and gains more ready access through the narrow micropyle than rigid solid bodies, including the shed exines.
6) shows how the ovule becomes inverted so that the micropyle points towards the cone axis, even though this axis may not extend above the insertion of the complex (Fig.
The sarcotesta in the region of the micropyle has a thickness that
the channel of the micropyle and diminishes from 9 [micro]m to 6
Surrounding the micropyle there are up to ten strata with
It is ultimately enclosed by one or two integuments, which develop from around the primordium base and encircle its apex, forming the micropyle.
However, in some tenuinucellate taxa, rapid and complete degeneration of micropylar megaspores and pressure from adjacent tissue soon results in a continuous subdermal nucellus layer at the micropyle.
Tilton (1980a) differentiated between a nucellar cap, which is rounded, and a nucellar beak, which is pointed and sometimes extends into the micropyle.
1985; Kolattukudy, 1980a, 1980b, 1981, 1984; Werker, 1980-1981) as well as the opening of the hilum valve (Hyde, 1954), the micropyle
or chalaza (Marchaim et al.
Microorganisms that infect seeds can enter through natural openings, such as the micropyle
, or through wounds or cracks.
the ovule is completely bent around so that the micropyle
faces toward the placenta.