The pollination - Orto botanico 'Pellegrini - Ansaldi'

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The pollination

Structure of the flower
The flower is the part of the plant that has the reproductive organs. In a lot of plants, the flower is the showier portion of the plant, even though it is ephemeral. From the outside to the inside, observing a flower, at first you notice the thistle, a shell of little foliaceous structures, the sepals, with protective function. And so it can be seen the corolla, usually very showy, composed of petals, with vexillate function, that is the task of attracting pollinating insects drawing them with their showy colours and with their particular shapes. The male reproductive organs are represented by stamens, composed of a filament and an anther, inside which the pollen is produced. The female reproductive organs are brought by the pistil, a structure generally central that includes the ovary, the stylus and the stigma; the latter is the part with the task of receiving and keep the pollen.
After the pollination and the successive fertilisation, the ovary will be transformed in the fruit, and the ovules contained in it will be semen.

Pollen carried by wind (I)
Oat (Avena sativa L.)
In some plants the transportation of the pollen does not occur through insects, but is up to the wind; these plants are called anemophilous; examples are all the species that belong to the family of gramineous plants, like the oat. In this plants, there is the reduction of the floral parts; there is no need of showy flowers because the pollen is carried by the wind. The plant produces more pollen, because probably a large part of it will be lost. It is also noticed an increase of the dimensions of the stigma, that in the gramineous plants is typically feathery, so it can more easily “capture” pollen grains suspended by the wind.

Pollen carried by wind (II)
Apuan willow (Salix crataegifolia Bertol.)
A lot of trees have flowers with separate sexes, that is they develop two different types of flowers,
the male ones that produce pollen and the female ones, that contain the ovary; the two different types of flowers can be brought onto the same plant or different plants: in the first case, we speak about monoecious species, in the second one of dioecious species.
The male flowers of many trees are gathered in elongated structures, that “dangle” letting the pollen produced is easily brought away by wind; these structures appear generally in spring and they are called “amentum” or “kittens”.

Pollen carried by insects (I)
The bastard balm (Melittis melissophyllum L.)
The flowers attract insects with attraction mechanism of two types: seduction, when the flower tries to attract the insect with something that can be useful for it, or deception, if the flower tries to attract the pollinator with a call that actually is not what it seems. A sensational example of deception there is in the orchids of the type Ophrys, in which a floral showy part, the labellum, simulate the female abdomen of a wasp insect. The males of wasp, that are attracted, perch on the labellum and they find themselves loaded of pollen, that then carry on the flower that visit later, making the pollination.
The insects are attracted by flowers for different reasons: a lot of insects eat pollen or nectar contained in the nectars, that occur for example in the Melittis melissophyllum L., others look for oils produced in the glandular hairs with which knead the pollen, others more are attracted by their smell, or their particular shapes and colourings. Instead, some types of corolla can offer shelter for the egg-laying and protection from adverse conditions.

Pollen carried by insects (II)
Orange lily
(Lilium bulbiferum L. subsp. croceum (Chaix) Baker)
In some flowers, like those of the type of Lilium, there are not the thistle and the corolla, but only one shell, called perigonium, composed of 6 elements called tepals, that are similar to petals.
The flower is open upwards; in the middle of the 6 showy orange tepals, with brown punctuations towards the base, 6 stamens are clearly visible, with big brown anthers with long filaments, and the pistil.
The pollination occurs with butterflies.

Evolutions of complex mechanisms
The marsh helleborine (Epipactis palustris (L.) Crantz)
In the orchids, the pollen is collected in a viscous mass and the reproductive organs are well protected and inaccessible to many insect species. Some orchid species attract insects producing a sugary liquid, the nectar, contained sometimes in a spur, like in the species of types Orchis, Dactylorhiza e Gymnadenia, or in a dome, like in Epipactis.
Attracted by the nectar, the insect perches on the labellum, and with his moves makes sure that the pollen masses stick to its head; with this valuable load the insect, putting himself on another flower always in search of pollen, “deliver” the pollen masses on the stigmas, making the pollination.
L'ORTO BOTANICO PIETRO PELLEGRINI, Un giardino alpino nel Parco Regionale delle Alpi Apuane
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