Plant Plumbing

xylemxylem experimentRed food colouring added to the water and taken up by a plant stem reveals the arrangement of xylem tubes in a cross section. Xylem tubes transport water up the stem from roots to leaves and flowers. These two stems had been left in the solution for two days.

Each yogurt drink container started out with 100 millilitres of water. As you’d expect, the daffodil took up more than the leafless stick of celery, eight millilitres as opposed to the five. There was no detectable evaporation from the container filled with water only.

Monocots and Eudicots

Two seed leaves of a dicot seedling emerging from a cushion of moss on the garage roof.
Two seed leaves of a dicot seedling emerging from a cushion of moss on the garage roof.
Wall barley, a monocot.
Wall barley, a monocot.

The experiment reveals that the xylem tubes in the daffodil, a monocot, are loosely clustered around the centre of the stem whereas in the celery, a eudicot, the xylem tubes appear more organised, arranged around the central pith along the edge of the stem.

Monocots are flowering plants that are so called because the emerging seedlings have one seed leaf (cotyledon). They typically have parallel veins in their leaves. Monocots include onions, bluebells, grasses and maize.

Dicots have two seed leaves and typically have a network of veins in their leaves.

Eudicot means ‘perfect dicot’. The eudicot clade (group) includes the majority of dicots but excludes basal angiosperms such as hornworts, water lilies, magnolias, avocado* and bay laurel, the herb that gives us bay leaves.

Deceptive Fruits

lemon avocado

megatherium
Avocado eating Megatherium from ‘The Golden Play Book of Animals of the Past Stamps’, a childhood favourite, and still there on my bookshelf!

*We’ve just returned from the farm shop and noticed that on our bill the assistant had misidentified the avocado (Basal Angiosperm;clade Magnoliidae; order Laurales) as a lime (Angiosperm; clade Eudicotyledonae; order, Sapindales). I can see how you could mix these up! We still think that the fruit on the right is an avocado but we won’t feel totally sure until we cut into it. The texture feels different to the lemon; it doesn’t have the same give in it, so it’s not ripe yet.

It’s been suggested that avocados evolved their fruits – which botanically are berries – containing one large seed, to be eaten by large mammals that have since become extinct, such as Megatherium, one of the giant ground sloths.

Links

I’ve been reading various books on botany and enjoying these two online resources:

From Roots to Riches: Our changing relationship with plants over the last 250 years – from tools to exploit, to objects of beauty, to being an essential global resource we have to conserve. Presented by Prof Kathy Willis. BBC Radio 4, Kew Gardens.

E O Wilson’s Life on Earth available as a free download from iBooks. Part 5 introduces Plant Physiology, which includes the experiment to demonstrate the properties of xylem.

Cannon Hall Farm Shop

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2 Comments

  1. I hope you let your readers know whether it was a lime or an avocado Richard, it will settle a difference of opinion in our house at least!

    1. It’s still not ready for eating. If only we had a pet Megatherium, it would be able to tell with one sniff. We’re heading back to the farm shop this morning so I’ll take a closer look. The limes were on the next shelf but they were all half the size of the lemons, and they were all streaky green unlike the sombre looking avocados.

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