Derek – Friday 26th February 2021

I took a photo of miniature daffodils last week but the picture showed flowers that didn’t look like miniatures, with nothing to judge their size by. So I had another go this week; I took a reel of cotton into the Garden and took a photo of the miniatures next to it. That didn’t work either, as the cotton reel is deceptive in size and appearance, and it was difficult to say exactly what it was, perhaps a mug.

I was once caught in a white-out on Ben Nevis. The ground was snow covered, the sky was white, and a fierce blizzard was blowing. It was impossible to tell whether a rock up ahead was a large rock a long way off, or a small one close by. The wind was so cold, I had to keep my head down, and when I looked up my companion ahead of me seemed to be in the sky. Our eyes are easily deceived without comparisons.

I had several more tries to get a photo of miniature daffodils. I tried snapping them next to a tape measure but, in the end, I settled for one with the miniatures growing next to a standard size daffodil.

All this had me thinking about size in plants and animals. There’s a lot of variation in size in nature, often with closely related species. A plant that intrigues me is the dwarf willow (Salix herbacea). This is tiny, just an inch or two high, growing in the Arctic or high in the mountains where there’s an Arctic-like climate. It is sometimes called the smallest tree but others won’t allow it as it is so diminutive. The dwarf willow is woody though, and like all willows is in the genus Salix. Its few inches can be compared to its taller siblings like the white willow, which can grow to 35 feet. But size isn’t everything, the dwarf willow is a great survivor, with large carpets of it in its tundra habitat.

The size of the dwarf willow has been brought about by adaption to climate. It grows in areas too cold for big trees. Where tall trees can grow, the limit on their size is gravity, as well as climate. Their increasing weight must be supported against the downward pull of the earth.

The maximum possible height for a tree is reckoned to be around 400 feet. The Californian giant redwoods (Sequoiadendron giganteum), also called Wellingtonia, get close to this limit. Large, mature trees are 90% dead, including oaks and beech, as well as the Californian giants. The living layer is just a few inches around the outside of the tree, just within the bark. The lifeless inner wood in the trunk functions as a skeleton to support the weight. But it is not simply weight which limits the height of a tree like the redwood, but also the difficulty of raising water to the canopy from the roots. The leaves become smaller (in this case needles) and ultimately lack of water halts further upward growth.

Large animals have bony skeletons to support them. Though a whale, in addition to its skeleton, is buoyed up by seawater. A beached whale soon dies, crushed by its own weight, unable to breathe. The hippo is the closest land relative to whales. Around 60 million years ago, the hippo ancestor (not actually a hippo) of the whale began foraging the sea for extended periods, probably coming back to land to mate, sleep and bear young. Ambulocetus, which means walking whale, is an ancestor of 40 million years ago: its fossils, found in Pakistan, still had legs. Many intermediary fossils have now been found until we get to the modern whale, so suited to its environment that Darwin had trouble persuading some of his contemporaries that whales were mammals and not fish.

The variation in dogs, in size and appearance, is staggering. The chihuahua is a miniature, weighing just five pounds. Compare this to the English mastiff which can weigh in at 300 lbs. Both dogs have developed from the wolf over the last 50 thousand years. Human selection supplanted natural selection to produce so swift a spectrum of canines.

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