Where do the plants come from?

The theory of spontaneous generation was quite a popular belief back in the day. It's quite easy to understand why people might have believed that animals could quite literally spontaneously come into being.

Take a larder full of food. Close the door and leave it for a few weeks, open it again and the larder may house various animals such as mice and cockroaches. Where did they come from if not from the ether? Of course we now recognise that these animals have actually migrated from outside the larder, attracted by the smell of the food, through small spaces. But it took a clever scientist to debunk the theory of spontaneous generation.

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The scientist was Louis Pasteur, of pasteurisation fame. He was interested in why food went off, due to the growth if mould. The popular belief was that the mould appeared spontaneously but he believed that the mould existed in the air and just grew when in contact with the food.

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His experiment was essentially very simple, but also genius. He cooked up a meat broth, the cooking meant that any microbes present in the food were killed. He then placed the meat broth into previously heated swan necked flasks. This design of flask incorporated an air trap to prevent the atmospheric air entering the flask and coming in contact with the broth.

The flasks were left for a period of time and no mould grew on the broth. He then broke one of the necks of the flask which allowed the air to come in contact with the broth and very soon after the broth went mouldy. A clear demonstration that the spores of the mould exists in the air.

As far as I know one of the sealed flasks still exists on display in Paris.

This week the idea of spontaneous generation is particularly easy to understand. It appears that with the warmth every patch of bare earth has suddenly become a carpet of green plants. They have appeared from nowhere. The damp earth, the Sun, the onset of spring have all acted as a catalyst for an explosion of growth.

Two weeks ago digging up that earth would not have yielded any visible plant material. Yet today the biomass is significant.

 

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