Pollination by the wind

This science blog investigates wind pollination by trees, flowers and grasses. We also take a brief look at pollination in water.Pollination needs to occur before fertilisation and plant reproduction can take place.

Pollination by the wind-trees

Wind pollination happens when pollen is carried from one place to another by the wind.

A good example of wind pollination can be seen in coniferous trees. Coniferous trees are ‘evergreen’ trees that grow cones.

Cones from coniferous trees come in all shapes and sizes…

pine cones of different shapes and sizes

Click on image for slide show

…but not all cones are as massive as this one from a 120 year old bunya pine tree in eastern Australia! Wear a hard hat when you walk through the forest!

bunya cone

Coniferous trees grow both male and female cones and it is only the male cones that release pollen. It is not difficult to identify which cones are male and which ones are female. The male cones are smaller than the female cones and often grow lower down in the tree.

  • Can you identify the male and female cones on the branch of this coniferous pine tree?

male and female pine cones on a pine branch

  • Which are the male and female cones on this mountain hemlock tree from Alaska?

Hemlock showing Female and Male Cones

 At certain times the male cones release millions of tiny grains of pollen which are carried upwards and away by the wind. What you see below is not smoke but a cloud of pollen grains released by the male cones of an evergreen ‘conifer’.  After they have released their pollen the male cones die and drop off the tree.

pollen from low hanging male cones of pine tree

When male cones on trees in a forest all release pollen at the same time the results can be quite spectacular!

pollen clouds

You can see a microscopic image below of grains of pine pollen.

  • Why do you think that each grain of pollen is surrounded by an ‘air bladder’?

microscopic conifer pollen grains surrounded by air bladders

After their release from the cones the microscopic pollen grains are carried upwards by the wind and the chances are that some will land on female cones higher up in the branches of other trees.

The pollination of a female cone is the first step towards ‘fertilisation’ and the appearance of pine seeds growing among the scales of female pine cones.

It can take two years after pollination for the female pine cone to produce seeds. You can see how pine seeds have grown between the scales of a female pine cone in the picture below.

Stone Pine showing nuts inside female cone

Pollination by the wind-flowers

The pollen from ‘ragweed’ is typical of wind borne pollen. It is very light; in fact it is far lighter than the sticky type of pollen picked up by insects, mammals and birds.

The pollen from ‘ragweed’ sometimes travels a very long way. It has even been found 400 miles out to sea. Below you can see ‘ragweed’ pollen magnified under a powerful electron microscope.

ragween pollen magnified under an electron microscope

  • Why do you think that a ‘ragweed’ has unscented flowers that do not produce any nectar? Why do you think that the flowers do not have ‘landing zones’?

common ragweedmicroscopy-uk.org.uk

The male flowers of a ‘ragweed’ face downwards.

  • In this picture can you see how some of the small flowers have matured and are ready to release their pollen?

ragweed with open flowers and stamensmicroscopy-uk.org.uk

The female flowers, on the other hand, face upwards. You can see the male flowers growing above the female flowers in this picture.

  • Can you see the stigmata hanging out of the female flowers ready to catch any wind borne pollen?

 ragweed showing female flowersmicroscopy-uk.org.uk

Pollination by the wind-grasses

The grass family contains over 9,000 different species found right round the world. Of these 9000 different species, we grow about 35 of them.

  • Can you think of some species of grasses that we grow? (*answers at bottom of page)

Grasses are the most widespread of all flowers on the planet and are absent from only two land masses in the world- central Greenland and Antarctica.

We don’t usually think of grasses as being plants that grow flowers!

zoysia grass flower

 Quite often we don’t get to see any of the flowers that grow on ‘stems’ of grass. This is because gardeners often cut the grass before the flowers are given time to develop. If you allow grass to grow on your lawn and stop mowing it you would eventually see ‘grass flowers’.

mower mowing a patch of grass

 Lawn grasses can spread without the need for their flowers to be pollinated. This happens when the stem of a grass plant grows both above ground and below ground. You can see this happening in the diagram below. Underground stems of grass plants are called  ‘rhizomes’  and ‘overground’ stems are called ‘stolons.’

structure of a grass plant showing stolons and rhizomes

 If you examine a magnified, uncut, wild blade of grass you may be able to see both the ‘stamen’ and the ‘stigma’. The stamens are exposed to the wind and the large feathery stigma are designed to catch pollen.

grass stamen and stigma

Pollination by water

Believe it or not sea grasses produce pollen from their tiny flowers! The pollen is transported to the stigma of other sea grasses by the ocean currents. Sea grasses (not to be confused with marine algae or ‘sea weeds’) grow in shallow waters on mud or sandy bottoms.

You can see the four main species of sea grasses below:

main four species of sea grasses

We don’t often get to see sea grasses, but they are very popular with dugongs. These ‘cows of the sea’ eat sea grasses much like cows and sheep eat grass on land!

dugong grazing on sea grass

 In fact, the pollinating sea grasses not only support the dugong but a whole eco system of different marine creatures.

sea grass ecosystem showing creatures it supports

*(species of grass cultivated by humans)including maize ,rice, wheat, barley, sorghum, millet, oats, wild rice, bamboo, rushes and lawn grasses.

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