Jan 04

Modular origami

A few months ago, I went to a creative origami lunchtime session organised by some lovely people at $WORK. I’d done origami a bit when I was younger, but mostly just frogs and cranes, which have since helped me while away the hours when invigilating exams. However, at this lunchtime session I was shown how to make modular origami. This involves making lots of (generally quite simple) origami parts, and then slotting them together to make larger structures.

Sonobe origami assembly [CC-BY-SA-3.0 Steve Cook]

I went home with a simple 12-unit Sonobe ball that afternoon and was very pleased with myself.

Cumulated octadedron (sonobe) [CC-BY-SA-3.0 Steve Cook]

Entry-level modular origami: the 12-unit Sonobe ball. Mathematically, it’s a cumulated octahedron; practically, it’s 12 sheets of square paper and about 1 hour of your time.

Things have rather escalated from there.

Assorted modular origami [CC-BY-SA-3.0 Steve Cook]

Between running some of these lunchtime sessions myself now, and being asked on several occasions on Twitter about how I make the pretty things I keep tweeting, I thought it’d be useful to put together a quick guide (or a link-farm, at least)..

Sonobe units are very easy to fold, quite forgiving, and can be used to make a cube (6 units), a cumulated octahedron (12 units), a cumulated icosahedron (30), and a kind-of truncated icosahedron (90, basically a spiky football). They’re a pretty good introduction to the general principles:

Assorted (sonobe) [CC-BY-SA-3.0 Steve Cook]

Sonobe family: 90, 30, 12, 6 and 3 units. The 3-unit one is a trigonal bipyramid but barely counts! These have all been made with the slightly modified unit mentioned below. The 90 units one is the biggest Sonobe that’s really worth making IMHO: about 3 hours’ work

The 30-unit ball has the symmetries of an icosahedron (or dodecahedron). Once you’ve learnt how to construct that object in Sonobe modules, you’ve essentially learnt how to construct any 30-unit modular origami ball: they mostly involve slotting 30 edge-units into groups of three to form the 12 pentagonal faces of a dodecahedron (or equivalently/alternatively, slotting them into groups of five to form the 20 triangular faces of an icosahedron – the difference is mostly one of perspective).

Cumulated icosahedron (sonobe) [CC-BY-SA-3.0 Steve Cook]

Cumulated icosahedron made of Sonobe units: 30 sheets of paper, and – if you’ve got the hang of the 12-unit ball – still only 1 hour of your time

There are lots of variations on the Sonobe unit you can (re)invent, by adding back-folds that expose the other side of the paper, or that make the tabs narrower than the pockets, giving a more intricate look.

Cumulated icosahedron (sonobe variant) [CC-BY-SA-3.0 Steve Cook]

Cumulated icosahedron made of slightly modified Sonobe units

Although the 90-unit structure is quite stable, the next one up (270 units) tends to sag under its own weight over time, but by that point it felt like a right of passage to make one.

270 (sonobe colourchange) [CC-BY-SA-3.0 Steve Cook]

9 hours construction, plus some planning. This uses duo paper, which is coloured on both sides, and a modified Sonobe unit that has a reverse fold to expose the other side of the paper in each module.

The Sonobe units can also be assembled inside-out to make inwardly cumulated polyhedra…

Cumulated postive negative icosahedra (sonobe) [CC-BY-SA-3.0 Steve Cook]

Getting the last few units in on the inverted ball (left) is tricky.

…and they can also be assembled in pairs and then assembled into a spiked pentakis dodecahedron...

Pentakis dodecahedron (sonobe colourchange pairs) [CC-BY-SA-3.0 Steve Cook]

Pentakis dodecahedron, with a reverse-fold Sonobe unit that shows the other side of the paper.

…and other structures.

Rhombic triacontahedron (sonobe colourchange pairs) [CC-BY-SA-3.0 Steve Cook]

Rhombic triacontahedron? Sort of. Has both colour-change and the units are assembled ‘inside out’ to make it inwardly cumulated.

The next unit I tried was the Penultimate edge unit (attributed to Robert Neal), which can be used to make a wireframe dodecahedron, as demonstrated by Matt Parker, the stand-up mathematician. Other variations of this subunit can be used to make pretty much any other wireframe polyhedron.

Dodecahedron (penultimate) [CC-BY-SA-3.0 Steve Cook]

Dodecahedron. I was trying to use up the boring coloured paper on this one, but I quite liked the result in the end!

Thomas Hull’s PhiZZ edge unit makes similar wireframe structures, but the modules fit together more tightly and the resulting structures are much more robust than you get with the penultimate modules.

Truncated icosahedron (phizz) [CC-BY-SA-3.0 Steve Cook]

Truncated icosahedron – this is basically the shape of a football (12 pentagons, surrounded by hexagons) and of some viral capsids too.

You can also make colour-change variants using the technique shown in Lewis Simon’s decoration boxes.

Dodecahedron (phizz colourchange) [CC-BY-SA-3.0 Steve Cook]

Dodecahedron made from PHiZZ units with a colour-change.

For structures based on dodecahedra/icosahedra and made from edge-units, you can always get away with using just three colours and never have two of the same colour pieces touching. This is because you can draw a Hamiltonian circuit on a dodecahedron: that is a path from vertex to vertex that only visits each vertex once, and which comes back to where it started. You can represent this in 2D on a Schlegel diagram.

Hamiltonian circuit through a dodecahedron [CC BY-SA 3.0 Tomruen/Steve Cook]

Hamiltonian circuit through the Schlegel diagram of a dodecahedron [CC BY-SA 3.0 original by Tomruen, modified by Steve Cook]. The red and purple edges form the Hamiltonian circuit; the grey edges are what is left over. You’ll notice that every vertex has one of each of the three coloured edges. The diagram is a projection of a dodecahedron: imagine taking a wireframe of the dodecahedron and shining a torch through it: the Schlegel diagram is the 2D shadow this 3D polyhedron casts on the wall. It’s fairly easy to work out which edge in the 2D diagram correspond to which edge in the thing you’re building.

If you colour alternate edges of the Hamiltonian circuit in two of your chosen colours, and the rest of the edges in the third, then you’ll avoid having any colour-clashes. I only learnt this after I started making these structures, so not all of them have this optimal colouring! The same 3-colour rule is true for the other Platonic solids, and also for the truncated icosahedron.

Francesco Mancini’s star-holes kusudama uses a similar module to the PHiZZ, but with a little back-bend that gives a nice 3D star effect. This one is a dodecahedron-shaped (30 units), but a 90-unit truncated icosahedron should also be possible.

Star holes dodecahedron [CC-BY-SA-3.0 Steve Cook]

Star holes dodecahedron.

Lewis Simon and Bennett Arnstein’s triangle edge unit can be used to make very nice patchtwork tetrahedra, octahedra and icosahedra.

Icosahedron (triangle edge) [CC-BY-SA-3.0 Steve Cook]


They’re a bit fiddly to put together but are very robust once constructed. A similar patchwork effect for the dodecahedron can be achieved with M. Mukhopadhyay’s umbrella module; Sonobe units can be used to make analogous Battenberg-cake style cubes.

Assorted (triangle edge sonobe umbrella) [CC-BY-SA-3.0 Steve Cook]

Battenberg-cake Platonic solids. The dodecahedron is made from umbrella units; the cube from Sonobe. The tetrahedron, octahedron and icosahedron are all made from triangle edge modules.

The simple isosceles triangle unit (attributed variously to M. Mukhopadhyay, Jeannine Mosely and Roberto Morassi) can be used to make small and great stellated dodecahedra.

Small and great stellated dodecahedron (isosceles) [CC-BY-SA-3.0 Steve Cook]

Great (left) and small (right) stellated dodecahedra.

The small stellated dodocahedron is particularly pleasing and makes a fairly robust decoration if made of foil-backed paper.

Small stellated dodecahedron (isosceles) [CC-BY-SA-3.0 Steve Cook]

Xmas decs

The great stellated dodecahedron can be made from the same subunit, but is tricker to construct because a tab has to curl around into a pocket that is partly inside the next tab round. I used needle-nosed forceps to construct this, and I’m still not terribly happy with the result.

The opposite is true for Paolo Bascetta’s star module, which makes a great great stellated dodecahedron, but a rather *eh* small stellation. This module needs duo paper (i.e. paper that is coloured on both sides) for best effect.

Small and great stellated dodecahedron (star) [CC-BY-SA-3.0 Steve Cook]

Great (left) and small (right) stellated dodecahedra.

Dave Mitchell’s Electra module can be used to make a icosidodecahedron: it’s unusual in that each module corresponds to one vertex of the structure: the edge units described up to this point combine together to make each vertex.

Icosidodecahedron (electra) [CC-BY-SA-3.0 Steve Cook]

Icosidodecahedron made from Electramodules

I’m not that happy with my Void kusudama (Tadashi Mori): I should have used duo paper, but it was really tricky to put together. Maybe one day. It’s one of the few structures here that is back to the original octahedral/cubic 12-unit structure. I’m not sure the 30-unit version would be stable.

Octahedral void [CC-BY-SA-3.0 Steve Cook]

Octahedral void

Tomoko Fusè’s little turtle modules are extremely flexible: they can be used to make pretty much any polyhedron that is made of regular polygons. However, because the flaps are only one paper layer thick, they don’t fit together terribly tightly, so I’ve only found them robust enough to make smaller structures without the help of glue. However, with glue, I’ve made a rhombicosidodecahedron, which is cool because it is built of pentagons, triangles and squares (all of the polygons found in the Platonic solids)…

Rhombicosidodecahedron (little turtle) [CC-BY-SA-3.0 Steve Cook]

The impossible-to-spell rhombicosidodecahedron.

…and also a pair of snub-cubes, which are even more interesting as the snub-cube has two non-superimposable mirror images, like hands, amino acids and amphetamines.

Snubcubes (little turtle) [CC-BY-SA-3.0 Steve Cook]

Snubcubes: left- and right-handed enatiomorphs.

I found Maria Sinayskaya Etna kusudama in Meenakshi Mukerji’s Exquisite Modular Origami book. It’s a really pretty model, and robust once it’s assembled, but it can be a bit fally-aparty during construction: I used very small clothes pegs to hold it together as I was making it.

Etna kusudama [CC-BY-SA-3.0 Steve Cook]

Etna kusudama.

Dennis Walker’s compound of five octahedra is also a bit fally-aparty, but I like it as – unlike many of these models – it genuinely is the polyhedron so-named, rather than something where you have to squint at the holes in the wire-frame and imagine faces there.

Compound of five octahedra [CC-BY-SA-3.0 Steve Cook]

Compound of five octahedra. You can easily see the yellow octahedron here: the sixth spike is underneath the model; the other four colours are similarly interlaced.

The five intersecting tetrahedra are actually a lot easier to make than they look. Francis Ow’s 6-degree modules themselves are easy to fold, and the vertices are a lot more robust than they might appear. The most difficult bit is getting the modules interlinked in the right way. I’ve managed it twice, but only whilst staring at the YouTube video and performing assorted “purple = green” gymnastics in my head.

Compound of five tetrahedra [CC-BY-SA-3.0 Steve Cook]

Compound of five tetrahedra – party piece.

Michał Kosmulski’s page has lots of lovely illustrations, instructions and inspirations.

This last one is a bit of a cheat as (in theory, and mostly in practice too) the structures above are held together by nothing more than friction. Valentina Gonchar’s revealed flower star kusudama has to be glued, which is kind-of cheating, but I couldn’t resist as it is two structures in one:

Flower star [CC-BY-SA-3.0 Steve Cook]

Revealed flower star – shut (left) and popped open (right).

Things I’d still like to do:

  • Build a much larger PhiZZ ball (270 units): this would be useful for demonstrating the structures of viral capsids.
  • I’ve not yet found a good great dodecahedron model: they exist on Pintrest, but I’ve yet to find any instructions for one.
  • I have lost wherever it was I found the instructions for this inwardly cumulated rhombic triacontahedron: I’d quite like to rediscover them so I can credit the inventor!
  • Invent my own module 🙂
Rhombic triacontahedron [CC-BY-SA-3.0 Steve Cook]

Rhombic triacontahedron of unknown source.

May 19

Organism of the week #31 – Tardigrades

Tardigrades make me squee. These little relatives of the arthropods and velvet-worms are found in the water around mosses, and they are quite easy to find if you have a cheap microscope and a little patience. Like spiders, they have eight legs, but unlike the legs of a spider, they’re plump and stumpy, and end in the little ‘fingers’ you can just about make out in the photos below. Ignoring the excess of legs, it’s easy to see why they’re sometimes called water-bears.

One of my first-year undergrads spotted this one in a sample of moss I pulled out of the down-pipe from my bathroom. The fact that my skin flakes and spittle contributed in some small way to this microteddy’s food-chain makes me feel about as paternal as it is possible for me to feel.

Tardigrades [CC-BY-SA-3.0 Steve Cook]

May 19

Organism of the week #30 – Sticky situation

All science is either physics or stamp-collecting.

This rather mean-spirited dismissal of chemistry and biology as “stamp-collecting” is attributed to Ernest Rutherford, the physicist usually (not wholly fairly) credited with discovering the atomic nucleus and the proton.

Shortly after Rutherford’s death in 1937, particle physicists discovered the muon, pi mesons, kaons, the electron neutrino, the anti-proton, the lambda baryon, xi cascades, and sigma baryons. It took physicists the thirty years following Rutherford’s death to make sense of this veritable album of subatomic stamps.

Nature has a sense of irony, but its comic timing needs work.

There’s nothing wrong with stamp-collecting. Science very often begins with stamp-collecting, because it’s only once you have enough stamps that you can start reliably identifying patterns in the stamps, and – from there – finding the interesting exceptions and edge-cases:

Baryon supermultiplet [CC-BY-SA-3.0 Studzinski.daniel]

Subatomic particle stamp-album [CC-BY-SA-3.0 Studzinski.daniel]

I have been an on-off collector of carnivorous plants since I was very little. Most of them attract insects, kill them, digest them to tasty soup, and then absorb that soup. The soup contains useful nutrients that are missing from the soil in which they are rooted, so this helps them grow and set more seed. But there are many plants that tick some of these carnivorous boxes, but not all of them. Roridula is one I’ve blogged about before: it subcontracts out the digestion part of the process to an assassin bug. Another plant that walks the line is a kind of passionflower:

Passiflora foetida bud [CC-BY-3.0 Alex Lomas]

Passiflora foetida bud

The charmingly-named stinking passionflower bears sticky hairs on tentacle-like growths around its flower buds. There is some evidence to suggest that these help protect the flower bud from hungry insects while it develops. Similar sticky hairs are also thought to protect the flower buds of a number of other plants.

The stinking passionflower kills insects, and even appears to digest them, but it doesn’t benefit from the nutrients this releases. However, it does benefit from not having its flowers damaged by herbivorous insects. This presumably means it sets more seed, so the ultimate effect – more baby plants – is the same as for ‘true’ carnivory.

Passiflora foetida flower [CC-BY-3.0 Alex Lomas]

Passiflora foetida flower. The reason these plants are called passionflowers is because the various parts of the flower are supposed to look like hammers, nails and a crown of thorns – items associated with the Passion (crucifixion) of Jesus – rather than the earthly passions you might have been considering

Is this plant carnivorous or not? Well, whether you ultimately choose to paste this stamp into the carnivorous plant album or not is very much less interesting than the reasons you have for making that decision. I’m just glad that someone discovered this particular stamp and took the care to stick it somewhere for us to study. Here’s to collectors and taxonomists, the unsung heroes of biology.

May 05

Adaptations evolve in populations

Organisms evolve adaptations to increase their fitness

There are few ideas in science that explain as much of the natural world as does natural selection, but there are few ideas in science that are more frequently misunderstood.

Often the misunderstandings are deliberate or disingenuous, but I’ve seen quotes like the one above even in undergraduate essays and popular science books.

There are two subtle problems with what is written above.

Firstly, adaptations do not evolve in individual organisms, because evolution isn’t something that happens to individual organisms. Evolution is something that happens to populations over time. A mutation that predisposes pea plants to making flowers that are purple will initially arise in a single, particular plant cell. But only if this plant’s offspring prosper (at the expense of peas with differently coloured flowers) will the population as a whole change over time.

Adaptations like flowers that attract pollinators – and the mutations that underlie them – arise in particular individuals, but they can only become more (or less) common in populations considered as a whole. Individuals mutate, but only populations evolve.

Biologists usually think of evolution as the change in frequency of an allele in a population over time. An allele is one of the various forms a particular gene can take. In the peas studied by Gregor Mendel, flower colour was determined by a single gene, which came in two variants: one variant – one allele – resulted in purple flowers, the other allele resulted in white flowers.

If – perhaps – the purple flowers were more attractive to pollinators like bees than the white, then the purple-flowered peas would tend to be fertilised more often, and would leave more offspring. The next generation of pea plants would then inherit a larger proportion of alleles causing purple flowers, and a reduced proportion of alleles causing white flowers. The purple allele would therefore increase in frequency at the expense of the white, and the population as a whole would become more purple over time.

Pisum sativum (white) [CC-BY-SA-3.0 Rasbak]

White-flowered peas (Pisum sativum) [CC-BY-SA-3.0 Rasbak]

Pisum sativum (purple) [CC-BY-SA-3.0 Rasbak]

Purple-flowered peas (Pisum sativum)  [CC-BY-SA-3.0 Rasbak]

For similar reasons, fitness is not a property of individual pea plants either; it is an average property of purple-flowered peas versus white-flowered peas. Any particular purple-flowered pea plant might get trampled by a cow and produce hardly any pea-pods; any particular white-flowered pea plant might get lucky and find itself in a cosy, well-fertilised spot near a beehive. But on average, the purple-flowered plants will do better and they will bequeath their purple-flower alleles disproportionately to the next generation: that is what we mean by the purple-flowered plants being ‘fitter’.

The second problem with the original statement is actually the smallest word: it’s that seemingly insignificant ‘to’. That ‘to’ is short for ‘in order to’, and there’s the rub. ‘In order to’ implies teleological agency and long-term purpose, which are not properties that you can reasonably attribute to natural selection.

Natural selection is a mindless algorithm, not a purposeful process. In essence natural selection is just this:

  • Organisms vary, and some of that variation is inheritable. Some peas have purple flowers, some have white, and this is (partly) due to purple- and white-flowered peas having different alleles of a particular flower-colour gene.
  • More offspring are produced than can survive and reproduce, so they will compete, and some variants will – on average – have greater success at making offspring than others. Pea plants produce more offspring peas than are ever likely to germinate, grow and get fertilised themselves. Some variants in the offspring may be better at competing for light, nutrients or pollinators: e.g. some flower colours may be more attractive to pollinators than others.
  • Those variants will contribute disproportionately to the next generation, and the frequency of their alleles will increase over time. If the purple-flowered peas are more attractive to pollinators, they will get fertilised more often, and contribute a larger number of seeds into the next generation. These seeds – and the plants that germinate from them – will inherit their parent’s purple-flower alleles, so we will see an increasing proportion of purple flowers as the generations tick over.
  • Rinse, repeat.

The match between the purple flowers and the purple preference of pollinators strikes us as clever and sensible and non-random, and it is all those things. But the process of natural selection that created this apparent design is just the mindless consequence of variation, heredity and differential reproductive success: it has no goals, no aims, no purpose.

Equally, this is a passive process for the pea population: they are subject to evolution by natural selection, but they are not active participants in the process.The peas do not strive supernaturally to make more purple flowers. The peas do not get magically instructed by the bees to make purple flowers. The peas certainly do not know what DNA sequences they would need to invent in order to make their flowers purple: new flower-colour alleles arise by mutation, which is just as mindless as natural selection, and even more heedless of what might be useful.

Populations do not evolve in order to do anything. Populations evolve, period. Purple flowers arise and become more common in pea populations because purple flowers happen to be attractive to bees; peas do not choose to evolve purple flowers in order to attract more pollinators. Mutation just throws up new alleles, and natural selection (and other important processes) make them more or less common over time.

It can become tedious describing this process passively and long-windedly every time: “purple flowers have become more common in the pea population because flower colour is highly heritable, and purple flowers are fertilised more frequently by bees”. If you want to write this more succinctly, you could say “purple flowers have evolved in peas because purple flowers are more attractive to bees” without loosing too much meaning.

Unfortunately, you might well see someone reword this as “peas have evolved purple flowers because bees prefer them”. This isn’t exactly wrong, but the ‘have evolved’ makes it sound very much like the peas are doing something actively, rather than having something done to them passively, and it’s all too easy to interpret this phrasing incorrectly. This puts us on the slippery slope to misconception.

If this is then reworded further to “peas evolved purple flowers to attract bees”, it sounds very much like like peas are active players in the process, and that they have a long term plan of improving their attractiveness to bees. This is almost guaranteed to mislead, unless you have your evolutionary biology filter turned up to maximum.

Do not write:

Some species evolved an adaptation to do some task

Write this instead:

An adaptation that does some task evolved in [a population of] some species

Given human nature (particularly on this subject), some people will still misinterpret your meaning, but at least you’re not implicitly misleading them with your language.

Jan 08


Recursion [CC-BY-SA-3.0 Steve Cook, Andreas Thomson, Frank Vinzent]

Recursion [CC-BY-SA-3.0 Steve Cook, Andreas Thomson, Frank Vinzent]

Jan 07


Bark [CC-BY-SA-3.0 Steve Cook]

Top left to bottom right: Betula utilis var. jacquemontii, Pinus sylvestris, Prunus serrula, Pinus pinaster, Quercus suber, Araucaria araucana, Metasequoia glyptostroboides, Pinus bungeana, Betula ermanii × pubescens, Pinus nigra ssp. laricio, Betula albosinensis cv. Red Panda, Platanus × acerifolia.

Jan 06

Wisley in Winter

It’s not really a botanic garden, but the Royal Horticultural Society’s gardens at Wisley is near enough as makes no difference. We visited in what should have been the dead of winter, but which in reality was this weird sprautumn mash-up that is now December in the UK. The heather garden was particularly pretty, despite the wind:

RHS Wisley heather garden [CC-BY-SA-3.0 Steve Cook]

RHS Wisley heather garden

At £12, the entry price is a bit steep: even Kew does reduced rates when most of the plants are underground, sleeping off the summer’s excesses.

Botanerd highlights included the biggest pine-cone I have yet added to my collection (yes, it is a collection, not a sickness)…

Pinus × holfordiana cone [CC-BY-SA-3.0 Steve Cook]

Holford pine (Pinus × holfordiana) cone – nothing satisfies like a 12 inch Pinus

…and the – apparently legal – purchase of class A drugs from the attached garden centre:

Lophophora williamsii [CC-BY-SA-3.0 Steve Cook]

Peyote cactus (Lophophora williamsii)

From what I gather, owning a peyote cactus is legal in the UK unless you ‘prepare it for consumption’, which magically transforms it into a 7 year jail term. This presumably includes accidentally letting it die and dry out into a button whilst on holiday. I may be having a teesy bit of buyers’ regret.

Jan 06


Most years the pond-water microscopy practical throws up an exciting ciliate (or two, or three), but this year, the only ones we saw were duplicates, or too bloody fast to photograph. Ho hum.

So this year you’ll have to make do with an imposter. It’s still got cilia, but it is not a ciliate, and although it’s no bigger than a single-celled organism, it is in fact a full-blown multicellular animal:

Euchlanis rotifer [CC-BY-SA-3.0]

Euchlanis rotifer

This is a rotifer (‘wheel animal’), which are famous for two things: being ridiculously small, and – in one infamous subgroup – being ridiculously averse to having sex. They’re also really cute when they turn on their feeding wheels. Happy New Year.

Dec 22

Bagging botanical Brussels

The last time we went to Brussels, I got terribly excited that the hotel we were staying in was right next door to the Botanical Garden of Brussels. Unfortunately – as we discovered in short order – at some point in the 1930s the plants had mostly been shipped off elsewhere, leaving the garden not very botanical, and Dr Cook not very impressed.

That elsewhere was the Plantentuin Meise / Jardin Botanique Meise, which is to the north of Brussels, conveniently situated – for the purposes of this second attempt to visit them – between Brussels airport and Antwerp.

Brussels botanic gardens [CC-BY-SA-3.0 Steve Cook]

Botanic Gardens, Meise

We were visiting in autumn, and they were in the middle of renovating part of their main glasshouse – the Plant Palace – but there was still plenty to see, including a good arboretum, an orchid exhibition, and some lovely Japanese beautyberries:

Callicarpa japonica [CC-BY-SA-3.0 Steve Cook]

Japanese beautyberry (Callicarpa japonica)

The entry fee (€ 7) is very reasonable, and the restaurant helpfully ensures all sandwiches come with a colonic depth-charge of salad; just the ticket to cure the faecal impaction resulting from the ‘food’ served to us on the flight out with <insert awful British airline here>. When we were there, there was also an art installation by Roos Van de Velde in praise of the best plant in the world – the maidenhair tree Ginkgo biloba  but you’ve only got until mid-January to catch it:

Gingko biloba Meise [CC-BY-SA-3.0 Steve Cook]

Roos Van de Velde’s Gingko biloba installation

Botanerd highlights:

  1. Whereas Kew’s evolution house (currently being renovated as part of the Temperate House restoration) always felt like a holding pen for a few cycads and ferns that didn’t physically fit into the Palm House, the Meise version was much more complete, with a good selection of horsetails, ferns, and high-quality fakes of fossil plants like Cooksonia, Lepidodendron, etc. That said, I would very much like to see these ‘evolution house’ efforts re-branded as ‘biodiversity houses’ or similar, as the usual Scala Naturae bullshit of using modern mosses, lycopods, ferns, and conifers as stand-ins for prehistoric forms gets right up my arse.
  2. The pinetum is small, but has a good selection of species, including quite a few weird cultivars of Japanese cedar (Cryptomeria japonica) that I’ve not seen before.

Cryptomeria japonica cv. Cristata [CC-BY-SA-3.0 Steve Cook]

Cryptomeria japonica cv. Cristata

Previous baggings…

Oct 06

Organism of the week #29 – Galling

Today is the first day of the new (academic) year at $WORK, but – aside from a couple of intro lectures – this is the calm before the real storm, which arrives in the form of a deluge of biological chemistry in November. If you’re lucky, you’ll get a few mugshots of some weird ciliate or other around then, otherwise, expect tumbleweed until the new (calendar) year…

Insects and flowering plants have been co-evolving for 200 million years or so, so it’s unsurprising that many of their interactions have become very intimate. The relationships between gall-forming insects and their host plants are particularly interesting. Gall-forming insects lay their eggs on plants, but when the larvae hatch, instead of munching through the plant in the usual fashion, the larvae make the plant build bizarre little houses for them. These are the galls. Galls provide protection from weather, some protection from things that might like to eat the gall-former itself, and food for the developing larva.

In the UK, there are many gall-forming insects that target oak trees. These are mostly very small wasps. One of the most obvious is the knopper gall, which are the sticky crater-shaped things you often see attached to acorns around August.

Rather like the fluke we met a few weeks ago, knopper gall wasps have a complicated life-cycle involving several different hosts, in this case two different species of oak: the English (Quercus robur) and the Turkey (Quercus cerris). Female wasps emerge in spring from the galls that fell from English oaks the previous autumn. These females then lay asexual eggs on the catkins of the Turkey oak, which hatch out, and form rather inconspicuous galls. The males and females that hatch from these galls in April then mate, and the females lay their eggs on the developing acorns of English oaks, where they develop into the knopper galls in late summer.

Andricus quercuscalicis on Quercus robur [CC-BY-SA-3.0 Steve Cook]

Knopper galls caused by the larvae of the wasp Andricus quercuscalicis, on oak (Quercus robur)

Like so many pests and diseases – the knopper gall is actually a fairly recent introduction: the first galls in the UK were recorded only in the 1950s.

Smaller but creepier, the silk-button spangle gall is a trypophobes’ delight. Like the knopper gall, they’re caused by small wasps, but are much less obvious until you flip a leaf over:

Neuroterus numismalis and Neuroterus quercusbaccarum on Quercus robur [CC-BY-SA-3.0 Steve Cook]

Mostly silk-button spangle galls caused by the larvae of the wasp Neuroterus numismalis, also on oak

The less creepy common spangle gall isn’t as likely to make you feel like you have maggots crawling under your skin, but like the silk-button spangles, that’s exactly what the plant has got.

Neuroterus quercusbaccarum on Quercus robur [CC-BY-SA-3.0 Steve Cook]

Common spangle-galls (Neuroterus quercusbaccarum) on – you’ll never guess what. There are a few older reddish spangles in the silk-button image above too.

The most famous and most useful gall found on oak is the oak apple. A mixture of mashed up oak apple galls and iron salts was – for a millennium and a half – what you dunked a quill pen into, if you were lucky enough to know how to write.

Oak apple [CC-BY-SA-2.0 Bob Embleton]

Oak apple gall: these are caused by the larvae several different species of by cynipid wasps [CC-BY-SA-2.0 Bob Embleton]

Like the knopper and spangle galls, oak apples are caused by the larvae of a tiny wasp, but it’s not just wasps that can cause galls, or indeed just insects. Roundworms (nematodes) can also form galls, usually on the roots of plants; as can some fungiMites, which are more closely related to related to spiders than to insects, are responsible for many galls of sycamores and other maples:

Vasates quadripedes on Acer saccharinum [CC-BY-SA-3.0 Steve Cook]

Bladder galls caused by the mite Vasates quadripedes on – gasp, not oak! – sugar maple (Acer saccharinum)

Aceria macrorhynchus on Acer pseudoplatanus [CC-BY-SA-2.0 Lairich Rig]

Mite galls caused by Aceria macrorhynchus on sycamore (Acer pseudoplatanus) [CC-BY-SA-2.0 Lairich Rig]

Why would a plant build a house for a parasitic insect or mite? The long answer is very long, but the short answer is that the parasite secretes plant hormones called cytokinins to manipulate the plant into forming the gall. In plants, cytokinins cause cell division and growth. They also act as “feed me” markers: sugars and other nutrients are preferentially directed towards tissues that have cytokinin in them. Cytokinins also cause plant cells to make red pigments. By secreting cytokinins (and other plant hormones) gall-forming insects, mites, fungi and nematodes manipulate the plant into building small – often red! – houses for them, and to supply those houses with sugar.

Zeatin [Public domain]

cytokinin hormone: the structure is a modified form of the DNA base adenine

The galls formed by insects and mites are amazing structures, but at a molecular level, the most extraordinary galls of all are formed not by insects or mites, but by bacteria:

Crown gall [CC-BY-SA-3.0 Bhai]

Crown gall on Kalanchoe, caused by the bacterium Rhizobium radiobacter (Agrobacterium tumefaciens) [CC-BY-SA-3.0 Bhai]

Crown galls may not look so impressive, but the way in which their inhabitants cause the gall to be formed most certainly is. The galls are formed by the bacterium Rhizobium radiobacter[For any biologists doing a double-take at this point: until recently Rhizobium radiobacter was known as Agrobacterium tumefaciens , but it’s been reclassified. This is Brontosaurus all over again…]

Rhizobium radiobacter is the world’s smallest genetic engineer. Rather than simply secreting plant hormones to make the plant direct food at it, like the gall-forming insects do, this bacterium actually injects a piece of DNA into the plant’s cells to bend them to its will. The DNA encodes enzymes for plant hormone synthesis, which causes the plant cells to grow into a cancerous mass: the crown gall.

But even that’s not enough for this bacterium. The nutrients directed into the gall by the plant are not quite to the bacterium’s taste, so the DNA it injects also encodes genes that turn plant cells into factories for bacteria-friendly food. This food even leaks out of the plant’s roots, feeding the bacterium’s sisters in the soil.

It took until 1982 for humans to develop the technology to genetically manipulate a crop plant to make better food. A mindless single-celled organism has been pulling off the same trick for millions of years. There’s nothing new under the sun.

Older posts «