Biology Reference
In-Depth Information
In most cases, however, the rapid depression of the anther cap was sufficient to
explain the movement of the pollinia onto the stigmatic surface.
Catling (
1980
) observed a similar mechanism in additional plants from York and
Simcoe Counties, Ontario, and from Cattaraugus County, New York, and Adams
County, Wisconsin. Here again, elevation of the anther cap led to a descent and rota-
tion of the pollen masses. Placed in insect-proof cages and watered from below,
these orchids showed levels of autogamy varying from 15 to 50%. Higher levels
were once more observed in a small sample treated with a simulated rain spray.
Catling's (
1980
) results are consistent with earlier observations by von Kirchner
(
1922
) on European plants of
L. loeselii
. Kirchner noted that the pollen masses
slipped out of the anther onto the column and the stigmatic surface without the par-
ticipation of a pollinator, but failed to note the role played by the elevation of the
hinged anther cap. Hagerup (
1941
), on the other hand, reported that the downward
movement of the anther cap expelled the pollen directly onto the stigmatic surface,
but considered that this movement occurred without outside influence. Neither von
Kirchner (
1922
) nor Hagerup (
1941
) associated the movement of the anther cap or
pollen masses with rain.
)NOTHER%UROPEANSTUDIES2EINHARDETAL
1991
) considered autogamy to be
obligatory, but Zeigenspeck and Kirchner (in Fuller
1966
) mentioned mosquito pol-
lination as a possible supplement to regular self-fertilization.
Reproductive Success and Limiting Factors
McMaster (
2001
), in Franklin County, Massachusetts; Wheeler et al. (
1998
), in East
Anglia (UK); and Jones (
1998
), in South Wales, reported high mortality rates in
populations of
L. loeselii
. The populations were short lived, expanding or disap-
pearing with changing conditions, and were maintained primarily by seedling
recruitment.
The level of seed production may, therefore, be critical. McMaster found that
51-77% of the flowers at his study site produced capsules over 7 years. These num-
bers correspond well with von Kirchner's (
1922
) report of self-pollination and cap-
sule development in 72 of 102 (ca. 71%) flowers on 20 plants. Seed count per
capsule averaged 4,270 and ranged from 1,601 to 11,748 for five capsules examined
during 1 year at McMaster's site. Extrapolation to the 551 capsules counted that
YEARGIVESATOTALESTIMATEOFOVERMILLIONSEEDSPRODUCEDINA¾MAREA2AMSEY
(in McMaster
2001
) determined that about 81% of the seeds were viable in one
natural population in England. Provided, then, that suitable conditions are available
for the establishment and development of new individuals, prolific seed production,
abundantly augmented by rain-assisted autogamy, may account for the continued
survival of
L. loeselii
populations despite short life spans for individual plants.
McMaster (
2001
) reported that well-watered, fertilized, and cultivated trans-
plants in partially shaded beds were significantly larger and produced many more
flowers than the wild populations, suggesting that drought, temperature, herbivory,
ANDORRESOURCESMIGHTBELIMITINGUNDERNATURALCONDITIONS2ESOURCESHOWEVER
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