A piece of my pink-flowering geranium broke off when the pot fell over. We put it in a vase, where it made new flowers that were red, not pink. What is going on?
J. A. Crofts
Nottingham, UK
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The plant is a zonal pelargonium, which is propagated by cuttings, rather than grown from seed.
The fact that the shoot broke off the main plant is irrelevant. The natural colour of the plant is bright scarlet from the pigment pelargonidin, but many new varieties are discovered as a result of genetic mutations, usually referred to as 鈥渟ports鈥�. Some mutations occur as a result of a minor change to a single gene in a single cell in the plant causing a change in colour, and in this case, the mutation caused it to look pink. However, in a particular plant, it is quite common for the mutation to reverse itself, in which case a part of the plant shows the original colour (scarlet). This is known as a sectorial chimera, where both colours appear on different parts of the same plant.
This situation can be a confounded nuisance to plant nurseries propagating choice variegated or bi-colour shrubs, since many of these may be unstable and give rise to a proportion of plants that don鈥檛 show the desired characteristics. A well-known example is golden privet producing green shoots.
David Muir
Edinburgh, UK
Many plants contain pH-sensitive coloured chemicals called anthocyanins. The colour of a hydrangea鈥檚 flowers can be affected by changing the acidity, or pH, of the soil in which it grows. Lowering the pH by adding acidic matter to the soil will make the flowers blue. Adding lime, an alkaline substance, will raise the pH and turn the flowers pink.
The geranium that your correspondent Dot Graham wrote in about belongs to the genus Pelargonium and contains the anthocyanin pelargonidin, which changes from red in acidic solution to blue in alkaline solution. I would suggest the water in her vase was more acidic than the soil in which the geranium was growing.
Fun can be had with anthocyanins. If you boil or steam red cabbage, keep the leftover liquid. It contains the anthocyanin pigment that gives the cabbage its colour. Impress a small child with your wizardry by pouring the cabbage water into three glasses: one containing a little white vinegar, which turns the water red; one with a little baking soda, which turns it green; and one with a little water, which maintains the purple colour with which you started.
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