Microscopes and Melissopalynology... what does a pollen grain look like?

Before ‘hayfever season’ begins, and while there is still frost on the ground, let’s talk about pollen. Pollen is a key component of bees’ lives, so we find it an interesting topic to research. It’s often seen
on the legs of our foraging bees, and our cats who come in from the garden in the spring and
summer with a fine dusting of it on their fur. Plus, of course, anyone sensitive to it will begin to
sneeze and/or get itchy eyes.

Pollen is vital to our world; every year thousands of different species of plants produce millions of
pollen grains. These are designed to be specifically distributed to reach their female counterparts
and so help proliferate the species. Thanks to Robert Hooke who invented the compound
microscope at the end of the 17 th century, the true nature of pollen was seen for the first time, and
instead of it simply being a fine dust, the grains could be individually identified. 

I confess that I didn’t know that pollen grains were different shapes and sizes. From my observation of our bees’ pollen loads I assumed they were all very small and round. We have been using a pollen identification chart which tells us, from the colour of the pollen, the plant from which it came. This has been useful as it has helped us to work out where the bees are foraging, how far they fly, and what they like to collect. The subsequent flower meadow we planted is a result of all this information; the bees told us how to retro-fit our garden to suit them.

Typically the honey our bees produce here at 13 Bees is fairly liquid, ‘runny honey’, and amber-coloured, a mixture of evaporated nectars from everything that grows here. Some years it is a little paler if the acacia has flowered well, other years it is darker due to the sweet chestnut in it. It is always called ‘mixed flower honey’ as a result, but a couple of years ago we harvested some
extremely pale, very sweet honey that crystallised quickly, so it was ‘set’ not ‘runny’. My curiosity was piqued: “what have our bees been collecting?” The surefire way to check this is to look at the pollen grains in the honey and thereby identify the plants that have been visited. So the first step was to collect pollen from those bee-friendly plants – off I went, wandering around our garden with tiny envelopes and small paintbrushes, tickling the insides of flowers to collect minute grains of pollen which I then peered at through my microscope. I was instantly lost in an incredible mini-verse of exines, intines, rods, apertures, furrows and lobes. Learning to recognise certain features of different pollen grains takes patience but I can now tell the difference between the pollen from a daffodil and that from a dandelion, and am thoroughly enjoying my foray into the world of palynology (the study of pollen and spores). 

Dandelion Pollen Grains

It’s relatively easy to match pollen to flowers when you know what you’ve picked (!), but looking at unknown samples is quite tricky. The world of melissopalynology (the study of pollen in honey) is absolutely fascinating and fairly complex. Honey pollen analysis involves identifying and counting pollen grains to determine the relative frequencies of each pollen type, so honey can then be categorised into mono-floral or multi-floral. To be mono-floral, eg labelled as ‘lavender honey’, there must be 45% or greater pollen grains from a single plant species. This is key to combatting fraud and inaccurate labelling of honey, but on a local or personal level, it is interesting and maybe reassuring to check exactly what kind of honey your own bees are making. 

 

 

Forsythia Pollen Grains

So far I have identified that the honey we harvested last summer shows our bees foraged on dandelions,
cherry blossom and acacia flowers, whereas the dandelion honey I bought from a market has more buttercup than dandelion in it! I shall continue with my studies and hope to build up a ‘library’ of reference slides so that later this year maybe I can check samples of our students’ honey to determine their bees’ floral sources. It should at least make better gardeners out of us!