Tuesday, March 30, 2010

Trees on the Move

Just outside the fence on the south-west corner of our garden there's a large Norway maple whose winged seeds are scattered all over our vegetable patch by south-westerley gales in autumn. All winter hundreds of seeds have been laying on the soil surface, buried by snow and dusted with frost crystals, and recently they've all begun to germinate, pushing out their first root into the soil. If we didn't cultivate this patch of ground every spring we'd have a small forest of Norway maple by now; some, behind the greenhouse, have escaped the hoe in earlier years and are on the way to becoming small trees.

Like many plants, the dormant seeds of Norway maple are incapable of germination when they're shed and it takes a winter's frosts to break down the dormancy compound - abscisic acid - inside the seed and allow germination to begin, just as the temperatures begin to rise in spring.

For more posts on tree ID click here

Sunday, March 28, 2010

Alive and Kicking

This weekend we walked past a derelict patch of rubble-strewn ground in Newcastle that was smothered in the golden yellow blooms of coltsfoot Tussilago farfara. This must surely be one of our most irrepressible wild flowers, since it seems to thrive on the most unpromising brown field sites and it only takes the merest hint of spring for its flowers to erupt through hard-packed ground. I once saw a newly created car park whose freshly laid, thick layer of  tarmac had been punctured by scores of coltsfoot flowers that had forced their way to the surface. The plant spreads via an underground rhizome that's full of starch and when the call of spring arrives it takes a lot more than tarmac to contain its pent-up energy. Coltsfoot's common name comes from the hoof-shaped outline of its leaves, while its Latin name Tussilago is derived from tussus, Latin for a cough; a mucilaginous extract from this plant has a long history of use in herbal medicine, as John Gerard noted in his herbal of 1597: "A decoction made of the greene leaves and roots, or else a syrrup thereof, is good for the cough that proceedeth of a thin rheume", he wrote.

Monday, March 22, 2010

How to talk to frogs

Just 10 days ago our garden pond was covered in a layer of ice. Yesterday I counted 44 frogs in it, wallowing in a sea of gelatinous spawn. They certainly haven't wasted any time in reproducing and they're still at it..... it's a bacchanalian orgy in there. This year I've covered the pond with a net, to ward of the predatory heron that wrought terrible havoc last year in the midst of all this amphibian lust.
.... meanwhile the spawn that has already been laid is beginning to develop. If you look closely at these eggs you can see a furrow across the centre of each. This is the first division of the fertilised egg, the first step on the road to it becoming a tadpole and then ....... if it's incredibly lucky, a frog. You can find a detailed illustrated description of the whole process, from fertilisation to froglet, here.
Yesterday I tried a little experiment that I've tried before... which always works. I used a portable recorder to record the frogs' mating calls, then played them back to them. The effect was instantaneous - 44 pairs of eyes swivelled in my direction and they all advanced towards the recorder. Intimidating.

Thursday, March 18, 2010

Shocking-blue Shell

We took some of our second-year students for a field trip to the coast at Souter Point near South Shields today and with 100 pairs of eyes scouring the rock pools they were bound to find some interesting marine life. Above is a blue-rayed limpet Helcion pellucidum, with shocking electric-blue stripes, that we found feeding on a kelp fronds. That iridescent colour is caused by microscopic, layered plates of aragonite in the shell that reflect back incident light waves so that they interfere with one another and produce the vibrant blue hue.

This delightful little mollusc, less than a centimetre long, is an Arctic cowrie, Trivia arctica - minute compared with its tropical cousins but equally exquisite in its shape and pattern.

Tuesday, March 16, 2010

Cautious Optimism

Blue skies and wild cherry buds showing the first signs of bursting, but this little huddle of still-hibernating 7-spot ladybirds Coccinella septempuncata don't seem to have got the message that spring has arrived .... or maybe they know something that we don't...

Saturday, March 13, 2010

Older Elder

Most elders Sambucus nigra growing in hedgerows never achieve much more than large shrub-size and are usually short-lived, but when this species does have space to grow it can become quite a handsome tree, with deeply fissured bark on its trunk. This individual (double-click for a larger image) grows beside the road between the Derwent reservoir and Blanchland and like many mature elders it's playing host to a dense covering of lichens on its branches and twigs, that look very attractive in the spring sunlight.

The yellow lichen is a Xanthoria species - probably Xanthoria polycarpa - that forms a dense covering on most of the older elder twigs.

Elder seems to be favoured host for this lichen - most trees seem to have some and many are smothered in it. I wonder what it is about elder bark that that makes it a favoured host?

For more posts on tree ID click here

Thursday, March 4, 2010

Liverworts on Springs

Liverworts are not, I have to admit, the most exciting plants - except when their spore capsules explode. These simple plants have been around for over half a billion years, confined to wet places like the muddy banks of streams, where I found this thalloid liverwort called Pellia epiphylla. Liverworts' common name derives from the fact that - if you've got a vivid imagination - their flat lobes look like lobes of green liver and since, according to the mediaeval Doctrine of Signatures, any part of a plant that looked like a part of the human body was supposed to be good for curing its ills, liverworts were assumed to be good for treating liver diseases. Superstition aside, liverworts become a little more interesting at this time of year when they produce these...
.. spherical spore capsules on the surface of the thallus. These change colour, from green to black as they ripen and then suddenly (for a plant) their stems elongate, often overight, raising the capsule aloft on a glassy stalk ....

.... then four vertical splits in the capsule wall become apparent and suddenly (this time, over the course of a few minutes) .....

... the capsule splits open, revealing a mass of green spores interspersed with strange whiskery golden threads.......

.... seen here at higher magnification.
You can see a short video of these writhing threads below .....

Here they are at higher magnification, along with a spore, and below....

... at higher magnification still, when it becomes apparent that each one of those golden threads, known botanically as an elater ...

.... has a helical spring embedded in it. Inside the ripe capsule the springs were all compressed but once the capsule wall splits their force is liberated, hurling out the spores until....

.... only 'springs' and a few remaining spores are left on top of the stalk. Meanwhile most of the spores...

... like this one, magnified here about 400 times, have been scattered to the four winds, to land on some muddy stream bank and germinate to form another thalloid liverwort. It's a cycle that's been going on for half a billion years and is repeated every spring.