Himalayan balsam nectar

 Himalayan balsam is notoriously invasive and the chances of ever eliminating it on a large scale seem negligible. Even when plants are pulled up there is always a large seed bank in the soil, and flooding carries the seeds far and wide along river valleys. But it does have at least one virtue: it's a very rich source of nectar late in the year, when few native nectar-rich plants are available. Bees and wasps find it irresistible.  

The flowers have a distinctive pollination mechanism, with anthers positioned in the roof of the flower, so they deposit pollen very efficiently on the upper thorax of visiting insects, like the honeybee above and the wasp below.

Persistent insect visitors are immediately identifiable by the dense coating of pollen that they carry from flower to flower - a very efficient pollination mechanism which goes a long way towards explaining the high levels of seed production.

Some balsam nectar-addicted visitors, like the wasp above, become so heavily coated in pollen that they develop a ghost-like appearance. 

Conifer pollen

The Korean fir Abies koreana in our garden has been releasing vast amounts of pollen over the last few days. 

These are the male, pollen-producing cones near the ends of the branches. Like all conifers it's wind pollinated and the pollen released is quickly diluted in an enormous volume of air, so it tends to be produced in great quantities. If you give the tree a shake it briefly hangs like a yellow cloud in the air.

These are the pollen grains under the microscope, magnified about 80 times.

If you look closely you can see that each pollen grain has two inflated air sacs, which are extensions of the pollen coat. These increase the surface area of the pollen with minimal increase in weight, so enhance its aerial buoyancy.

Click here for more on conifer pollination.

This is where the pollen grains are heading - the new female cone at the top of the tree. Only a few of the pollen grains will successfully complete their journey and fertilise the female ovules, which are arranged in pairs on the upper surface of those whorls of cone scales.

At this time of year they are an attractive shade of purple but by autumn, as they seeds develop, they become brown and then break up through the autumn. Coal tits are particularly partial to the seeds - click here for photographs of them picking the cones apart.

Meadow foxtail

For hay fever sufferers the season of misery has arrived, and this is one of the culprits – meadow foxtail grass Alopecurus pratensis. The flower spikes produce their feathery stigmas from each floret first (bootom picture), then the dangling stamens are produced from the top of the flower spike downwards (top picture), releasing clouds of minute pollen grains as they split open. Some pollen grains are filtered out of the air by those feathery stigmas, which you can see under the microscope at my other bog Beyondthehumaneye

Meadow foxtail is very similar to Timothy grass Phleum pratense and the easiest way to tell them apart is by flowering time – Timothy doesn’t begin to flower until July, after spring-flowering meadow foxtail has finished.