Red 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
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
*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.
The stem of the bush in the top right corner of my drawing is elder, another plant with similar looking leaves. Glossy bluebell leaves are springing up but wood anemone and wood sorrel have yet to appear.
‘I always come down it!’
Hairy bittercress, Cardamine hirsuta, reminds me of a small version of lady’s smock, Cardamine pratense. It’s one of the earliest of weeds to flower and one plant can produce 50,000 seeds.
Thinking of spring, we’re planting bulbs. The crocus bulbs are already putting out shoots, the Eranthis, better known as winter aconite aren’t showing signs of life but they should flower before the crocuses.
The winter aconite ‘bulbs’ are actually corms, swellings of the base of the stem of the plant. A bulb is a short stem surrounded by fleshy leaves or leaf bases.
We take a walk around the Woolley Colliery site on our Wakefield Naturalists’ Society midsummer field excursion. I remember this being a grey spoil heap in the 1980s but it’s now fully restored. Hundreds of orchids are in flower on the grassy slope including plenty of bee orchids, a species which I don’t remember having seen before.
