Doing Darwin’s Experiments: Flytraps and Sundews Understanding Letters: Questions and answers Base your answers on the following




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Doing Darwin’s Experiments: Flytraps and Sundews

Understanding Letters: Questions and answers
Base your answers on the following:

Letter 2886: Charles Darwin to Joseph Hooker, 31 Aug, 1860

Letter 2908: Charles Darwin to Joseph Hooker, 6th Sept, 1860

Letter 2913: Charles Darwin to Daniel Oliver, Sept 11, 1860

Letter 2921: Daniel Oliver to Charles Darwin, 19 Sept, 1860

Letter 2941: Charles Darwin to Daniel Oliver, 29 Sept, 1860

Extracts from: ‘Insectivorous Plants’, Charles Darwin, 1875 on Drosera rotundifolia and Dionaea muscipula
1. Why do you think Darwin was so curious about insectivorous plants? Why does he call the plants ‘first rate chemists’?


  • Letter 2886: Darwin writes that he is ‘very curious’ about ‘the rate of closing of leaves of Australian Drosera.’

  • He calls the leaves ‘first rate chemists’ because they ‘can distinguish even an incredibly small quantity of any nitrogenised substance from non-nitrogenised substances.’

  • He is fascinated by how much ‘nitrogenised substance’ (i.e., animal matter) is needed to cause leaf movement in Drosera.

2. Describe the kinds of experiments that Darwin conducted. What tools did he use to conduct his experiments?



  • He used every day materials: milk, olive oil, and egg whites (also called albumen) to test Drosera’s movement.

  • In ‘Insectivorous Plants,’ Darwin describes using half roasted meat, roasted beef, and cheese to see what Dionaea most effectively digests.

  • Letter 2908: Darwin reports that he has tried 14 fluids, putting a little fluid on ‘several leaves’ to see if the ‘leaves or hairs’ move at all.

  • While fluids without nitrogen (e.g., water, syrup of sugar, starch, etc.) don’t cause the leaves to move, fluids with nitrogen (milk cold fusion of raw meat, urine, raw white of egg, etc.) do.

3. What questions did Darwin ask his colleagues? How did his colleagues describe their own experiments?



  • Darwin used his letters to describe his own experiments with plants and to ask colleagues to conduct experiments on his behalf.

  • Letter 2913: Darwin asks the botanist Daniel Oliver both to observe the ‘rate of closing of leaf’ of Drosera and also whether the hairs of Drosera are ‘viscid,’ or sticky.

  • Letter 2921, Daniel Oliver responds to Darwin’s query with the results of his experiment. He gives a full description of his experimental protocol and concludes that ‘gum drops’ cause the hairs on the Drosera leaves to move the most.

  • Letter 2941 Darwin writes to Oliver to ask if a living Dionae could be sent to him at Down House, to observe its structure. Darwin says: ‘How I should like to see a fly caught by it!’

4. Compare Darwin’s letters on sundews and flytraps to his published book, ‘Insectivorous Plants.’ What are the similarities and differences?



  • Darwin’s letters give a good of a sense of Darwin as an individual. He often inquires after his correspondents’ family members and writes with a lively style.

  • In his published writing his style becomes more formal. It is also clearer what big questions Darwin wants to answer using his experimental results.

  • In ‘Insectivorous Plants,’ Darwin suggests that he is using his experiments to better understand how insectivorous plants are ‘excellently adapted for the special purpose of catching insects.’

  • Drosera excerpt: Darwin explains his goal in studying this species to understand how it developed adaptations (like the ability to move its leaves in response to animal matter and to use sticky hairs to trap animal prey).

  • Dionaea excerpt: Darwin uses experiments to illustrate how Dionaea digest food.

  • Published excerpts show how Darwin’s interest in insectivorous plants can be seen as an extension of his previous work on evolution of animals and humans in ‘On the Origin of Species’.



Doing Darwin’s Experiments - Survivor Seeds

Understanding Letters: Questions and answers
Base your answers on the following:

Letter 1762: Edward Blyth to Charles Darwin, 1-8 Oct, 1855

Letter 1962: Charles Darwin to Philip Henry Gosse, 28 Sept, 1856

Letter 668: Charles Darwin to John Lindley, 8 Apr, 1843

Letter 1783: Charles Darwin to Gardeners' Chronicle, 21 Nov, 1855

Letter 353: Charles Darwin to J. S. Henslow, 28 Mar 1837

Letter 1661, Charles Darwin to J. D. Hooker 7 Apr 1855

Letter 1667, Charles Darwin to J. D. Hooker 13 Apr 1855

Letter 1669, Charles Darwin to J. D. Hooker, 19 Apr 1855

Letter 1681, Charles Darwin to J. D. Hooker,15 May 1855?

Extracts from Darwin’s experiment book
1. What kind of information was Darwin gathering about seeds surviving extreme environmental conditions?


  • Letter 1762: Darwin is interested in how farmers use heat to ‘accelerate the germination of the haw-seeds.’ He wonders what would happen if he fed a turkey haw seeds – would the turkey’s body heat cause the seed to germinate?

  • Letter 1962: Darwin is gathering as much information as he can about how seeds might be transported to ‘distant islands.’ Could they float in the ocean or be carried in the mud stuck on ‘birds’ feet or base of beak’?

  • Letter 668: Darwin reports that there are some seeds which successfully germinated after being found ‘in a layer under about 25 feet thickness of white sand’ located ‘on the margin of an anciently existing lake.’

2. Describe the experiment that Darwin conducted with saltwater and seeds. What types of seeds did Darwin use?




  • Letter 1661: Darwin reports he has started his experiments and asks how long Hooker thinks these seeds might survive in sea water.

  • Letter 1667: Darwin describes his experiment. He has seeds submersed in salt water at 32-33 degrees Celsius. He also has seeds in ‘small bottles out of doors, exposed to variations of temp’. After being immersed for one week, all have germinated. He wants to figure out whether or not these seeds could survive a journey in the Gulf Stream of 50-60 miles a day.

  • Letter 1783: Darwin writes to Gardeners’ Chronicle detailing the results of his experiment. He also lists the types of seeds he uses: capsicum, canary seed, celery, oats, spinach, onions, beets, potatoes, lettuce, carrot, radish, etc. They are all seeds that one could find easily at a garden centre.

3. What were some of the problem’s Darwin faced with his experiments?




  • Letter 1669: Many of the seed bottles are starting ‘to smell horribly’ if the water isn’t changed every day. Also, the cabbages and some of the radishes are dead after being soaked in salt water for 14 days.

  • Letter 1681: ‘The fish at the [Zoological Society] ate up lots of soaked seeds’ and then ‘the fish ejected vehemently…all the seeds from their mouths.’ The implication of this observation has to do with Darwin’s theory of animal-supported seed dispersal. Darwin predicted that the fish (with the seeds in their stomachs) would be eaten by birds; these birds would then fly to a remote island; upon landing, they would excrete the seeds, which would germinate. Given the behaviour of the fish at the Zoological Society, Darwin’s prediction proved incorrect.



Doing Darwin’s Experiments - Weed Garden

Understanding Letters: Questions and answers

Base your answers on the following:

Letter 2067, Charles Darwin to Joseph Hooker, 21st March, 1857

Letter 2075: Charles Darwin to Joseph Hooker, 12 Apr, 1857

Letter 2101: Charles Darwin to Joseph Hooker, 3 June, 1857

Extract from Darwin’s Experiment Book

Extract from ‘On the Origin of Species’, Charles Darwin, 1859


1. Using Darwin’s letters to Hooker, describe Darwin’s weed garden experiment. For more information about Darwin’s experiment, consult the excerpt from Darwin’s weed garden experiment notebook.

  • Darwin wrote many letters to his good friend Joseph Hooker who was a botanist at Kew Gardens. In this series, Darwin describes his “weed garden” which is “32 square feet” and located on the grounds of Darwin’s home at Down House. Every time a weed seedling starts to grow in this patch, Darwin recorded its appearance. He then regularly returned to his weed garden to record whether or not these seedlings have survived. Darwin reported to Hooker that out of 357 weed seedlings, 277 were killed by slugs.

2. Which results from Darwin’s weed garden experiment does Darwin seem most surprised about? For more information about Darwin’s results, consult the excerpt from Darwin’s weed garden experiment notebook.



  • Darwin remarks in Letter 2075 that he had expected less seedlings to be killed by pests like slugs, writing “I had fancied that this was a less potent check than it seems to be.” In his Experiment Book, Darwin concludes that between 1/5 and 1/6 seedlings survived the summer.

3. What kinds of problems seem to plague Darwin’s weed garden the most?


4. Describe what scientific concept you think that Darwin was testing with his weed garden.



  • Darwin wanted to know what environmental conditions made a seedling most likely to germinate with success. He concludes – as seen in the excerpt in this pack from ‘On the Origin of Species – that seedlings will be more successful if planted in the soil away from other plants. Even within a small plot of land, then, Darwin observes the competition between plant species for a limited amount of resources.


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