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A seed of an idea

Back from the Beagle, Darwin

pondered how plants and animals

reached all the corners of the Earth.

Conventional wisdom was that God

put them there, but Darwin had

other ideas. Perhaps seeds survived

at sea and used ocean currents…

You will need:

Seawater (most pet shops sell salt

water), glass jars, your choice of

seeds, a sieve, plant pots, compost

Darwin used seeds of cress, radish,

cabbages, lettuces, carrots, celery

and onion. Label jars, fill with

seawater and your seeds. After

seven days, put the seeds in a sieve,

rinse under a tap, and plant out in

labelled pots. Darwin also studied

longer periods in seawater, the

effects of water temperature on

germination, and whether seeds

float. His experiments overturned

the idea that seawater kills seeds.

Of the 87 species he used, Darwin

found almost three-quarters could

tolerate at least 28 days in salt water.

Dying young

Darwin set up his “weed garden”

experiment in January 1857, but if

you set about this soon you’ll still

get good results.

You will need:

A tape measure, four pegs, a

hammer, a ball of twine, a spade,

a ball of garden wire snipped into

5-centimetre lengths

Use the pegs and twine to mark

out a plot of lawn (1 metre by

0.7 metres) and carefully remove

the layer of turf to expose the soil.

Return every day to check for signs

of germinating seeds, sinking a small

length of garden wire next to each

emerging shoot and collecting up

(and keeping) wires where seedlings

have died. Come summer, work out

the extent of death on your patch.

Darwin found that more than 80 per

cent of his weedlings died young.

Hungry plants

Just after the publication of

On the Origin of Species,

Darwin was on holiday in the

neighbouring county of Sussex

when he stumbled upon the tiny

insect-eating plant Drosera

rotundifolia or sundew. This inspired

him to mount a series of detailed

experiments to discover its

preferred diet.

You will need:

A sundew plant,

pretty much any food you like

Darwin tested the sundew’s

appetite for a vast array of different

foods, including milk, oil, egg white,

gelatin, sugar, hair, toenail clippings

and even drops of urine. Make up

your own morsels to discover what

the plants like and dislike. Darwin’s

conclusion was that they were

seeking out nitrogen.

If you can’t get hold of a sundew,

you might try experimenting with a

venus flytrap to see what triggers

it to snap shut.

Guided by the light

Darwin noted that plant shoots

emerging from the ground were

sensitive to light and bent towards

the sun as it crossed the sky. Keen

to find out how the plants managed

“directed“ movement, he and his

son Francis experimented.

You will need:

Plant pots, soil, seeds (Darwin used

canary grass, Phalaris canariensis),

aluminium foil, a lamp

Sow the seeds in pots. When the

shoots emerge, switch on the lamp

and watch them grow towards it.

Repeat, but this time pop a foil “hat”

securely over the tip of the shoot

before switching on the lamp.

Darwin worked out that the upper

part of a shoot is necessary for

the plant to respond to light: this

paved the way for the discovery of

plant hormones.

14 February 2009 | NewScientist | 45

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to test whether bees were needed to fertilise clover, using mesh – made from his wife Emma’s old petticoats – to deny insects access to flowers in one of his meadows.

With only three episodes to cover a life’s work, the programme makers were forced to cherry-pick, but they could have done more to acknowledge the large number of experiments left out. When it came to seed-salting, for example, Darwin didn’t just pop six species in salt water, he ran dozens of experiments. When his seeds sank it seemed to pose “a fatal obstacle” to ocean distribution. So he investigated seed buoyancy. If really dry, many seeds will float.

Though we get only a slice of Darwin the experimentalist, Doherty is an enthusiastic presenter, interspersing daily

life at Down with vignettes about Darwin’s experiments on orchid sex, the diets of carnivorous plants, worm intelligence and human emotions.

One of the charms of the Down House experiments is the way Darwin used common or garden species and household items, and frequently involved members of his family. Re-enacting them is a fantastic way for us all to find out where scientific inquiry can lead – and it offers a unique insight into the influential and honest Darwin. We have four experiments here, and there are more online. ■