TODAY’S topic has fascinated me since childhood – how do seemingly flimsy plants manage to drill through solid tarmac as if it is butter?
Looking this up on the internet, I found that the majority of articles insist that plants cannot do this but are exploiting microscopic cracks. If seeds germinate and the roots can find water the plants will survive and grow. This may be true for concrete, but I am certain that some plants, if they are covered by tarmac, are capable of forcing their way through. I have seen this a lot with dandelions coming through tarmac. There is first a slight mound which grows until it cracks open at the top and the leaves come through. Near here there are some creeping thistles shooting through tarmac laid about two years ago. I found it hard to take pictures that show what I could see, which was bits of tarmac thrust to one side, but here is an effort.
This is a close up of the plants at the top left of the picture.
As to how they do it, I have spent some time poking round the internet and I am not a lot wiser. I found these comments on Reddit:
‘If I remember correctly, plants being able to grow through concrete has a lot to do with the Sclerenchyma cells/tissue, specifically the sclereids and fibers. They are essentially dead, tightly compacted protective/supportive cells that are super duper strong. When a plant grows towards something such as concrete, these cells are the driving force that breaks into the concrete and eventually pushes/grows through.’
‘Asphalt isn’t a hard material. It feels hard as the material beneath it is. It’s a lot easier to push up out of the asphalt than push down into it.’
And this on Quora:
‘Asphalt upon being laid is rolled flat under pressure so that the visible surface looks homogeneously smooth, but in the process of flattening shear zones of weakness are produced. Asphalt absorbs sunlight and heats up causing it to expand and then at night to contract. With subsequent weathering, those zones gradually enable entry of air and water, eventually leading to formation of fine cracks. Plants even when kept in darkness have exceptional ability to exert upward force through their own internal turgor pressure. So, when small seeds filter through an asphalt crevice and then germinate, they grow back toward sunlight. The same thing happens on rock faces. Moisture is essential, but in the case of asphalt its ability to warm up gives the plants a real growing boost.’
Anyway at least I did find a few comments which agree with me that I haven’t made up the whole idea.
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A few pictures from the week. First the largest patch of lords and ladies (Arum maculatum) seeds that I’ve ever seen. Usually they seem to be on their own.
I am pretty sure the tree below is an elder (Sambucus nigra) but I cannot find out what the lumps on the branches are.
Lastly, a spectacular spear thistle (Cirsium vulgare) which I wrote about in this article.
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Sheep of the Week
Photo: Attiewestraad, CC BY-SA 4.0, via Wikimedia Commons
This must be one of the most easily recognisable sheep. The Dorper was developed from the 1930s in South Africa using various crosses to create a meat sheep suitable to the more arid regions of South Africa, with a self-shedding coat so that it does not need shearing. In 1942 the South African Department of Agriculture settled on crossing Dorset Horn rams imported from England with Blackhead Persian ewes, which despite the name originally came from Somalia. (The name ‘Dorper’ comes from ‘Dorset’ and ‘Persian’, though apparently there was a dispute as some early breeders favoured ‘Dorsian’.)
This is a Dorset Horn, which I wrote about here.
And these are Blackhead Persians:
Along the way white sheep were produced, which are called White Dorpers. They are not recognised as a separate breed.
The new breed turned out to be adaptable to other climates as well as dry ones and is now widely farmed in the US, South America, New Zealand, Australia, Europe and Asia.
The first Dorpers in the UK were imported from New Zealand in 2004 by a Berkshire organic farmer, Bernadette Dowling of Cranes Farm, East Garston, near Hungerford, thus bringing back the genetic heritage of the Dorset Horns which went to South Africa 70 or so years earlier. The flock’s first lambs were born in September 2005 and the British Dorper Sheep Society was formed soon afterwards.
The Dorper is increasingly popular in Great Britain and the Dorper Society believe it has the potential to be the leading sheep breed here. Their website says: ‘Even though the UK already has some excellent terminal sire breeds available to sheep farmers, some of these breeds have lambing problems, producing additional veterinary expenses. Dorper births are usually completely trouble free due to their light bones, and with their dense hair coat, natural hardiness and amazing vigour they quite literally “hit the floor running”. Most lambs are on their feet within five minutes of birth, and suckle within 15 minutes.’
The ewes can lamb more than once a year, while rams reach sexual maturity at an early age and have been observed ‘working’ by five months.
One distinctive feature is that the Dorper’s skin is twice the thickness and strength of most other breeds. In South Africa the hides are sold as top-quality leatherunder the name ‘Cape Glovers’ and represent about 20 per cent of the total carcass value.
I couldn’t find any very interesting videos of Dorpers – this is the best I could do.
But while I was roaming around YouTube I found this enchanting tiny clip.
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Wheels of the week
THIS is a 1995 TVR Chimaera 3952cc. The road to its production could fairly be described as rocky.
The firm was founded by Trevor Wilkinson (1923-2008), who was born in Blackpool and left school at 14 to start an engineering apprenticeship at a local garage. In 1946, when he was 23, he bought a disused workshop in Blackpool and started a general engineering business which he called Trevcar Motors. Much of his work was repairing funfair rides, and the following year he took on car enthusiast Jack Pickard as a partner and changed the firm’s name to TVR, a contraction of Trevor.
In his spare time Wilkinson built himself a sports car with an aluminium body on the renovated chassis of an old Alvis. It took him two years, after which he built another car from scratch, designing the chassis and suspension himself. He incorporated a Ford engine, Morris Eight wheels and back axle, and bits from old dodgem cars. A cousin bought it from him for £325 (about £9,500 now).
The first quasi-‘production’ car was the TVR Sports Saloon in 1954, with an Austin A40 engine and a plastic kit car body.
By 1958, the TVR Grantura (meaning grand tourer, or GT) was revealed in customer-ready form – a squat coupé featuring a wide choice of engines and huge wire wheels.
However Wilkinson was apparently not much of a businessman, and by 1962 the company was in financial trouble. He had also got involved with a whole range of partners and in the end felt they were undermining him. He quit in April 1962, and Pickard also left. In December 1962 TVR went into receivership but staff and directors kept it going and work started on the Griffith 200, based on the Grantura. In 1965 TVR went bust, and Arthur Lilley and his son Martin purchased the assets of TVR to mitigate their personal losses of £2,000 worth of TVR shares.
There were an incredible number of TVR models, some being produced in tiny numbers (Wikipedia lists 59.) At the Earl’s Court Motor Show in 1970, TVR garnered much publicity by having a nude model on the stand. The following year they had two, as you can see here. As no doubt intended, the Society of Motor Manufacturers and Traders threatened to ban TVR from the show.
In 1980 the rather odd-looking Tasmin was released. Sales were lacklustre, coinciding with recession in the UK, and the result was that TVR was again on the brink of financial collapse.
From 1981, the business footing of the company was steadied after millionaire TVR devotee Peter Wheeler took control. It was under his leadership that the TVR Chimaera came into being. The name was derived from Chimera, the monstrous creature of Greek mythology made of the parts of multiple animals. It was launched at the 1992 Earl’s Court Motor Show and was manufactured until 2003. A total of 5,256 were made. The model I saw is a 4.0 which has a 0-60 speed of 5.1 seconds, and a top speed of 152mph.
TVR has lurched through various crises since but is still producing cars. In a nod to earlier days, the current model is the Griffith V8, which you can see here.