Tag Archives: Mendel

Light and dark: Mirabilis jalapa – Belle de nuit


My neighbour and I were very happy to discover this plant growing at the foot of the wall of the garage that we share, and since then we’ve been looking after it tenderly. It’s an unusual flower coloration for our village – almost all others are red or yellow, and you can have both on the same plant.   It seems to love cracks at the edges of roads or pavements, growing up fast in mid to late summer and in full bloom at the moment. The plants grow from tubers, like dahlias, and can also reseed, thus quickly becoming invasive once established. It’s a garden escapee, now naturalised.

One English name is the four o’clock flower, and the blooms do indeed open late in the afternoon –  earlier on grey days  –  and stay open all night to attract moths. The plant originates in Peru, and this nocturnal habit is an adaptation which is more common there or in Mexico (Jalapa is a Mexican town), where temperatures can be too hot for a flower in the daytime.

The plant has some significance to botany since it was studied by Carl Correns, who was one of the rediscoverers of Mendel’s genetic laws in 1900. Correns researched into the causes of the variegated leaves of some plants of M. jalapa and showed that the white mottling was a characteristic inherited from the seed (‘mother’) plant, rather than from the pollinating plant.  This was the first demonstration of cytoplasmic inheritance: the fact that all sexually reproducing organisms from pine trees to humans inherit DNA from both male and female parents, but can also inherit factors in the cell from the female line only.  In the case of plants, this inheritance includes the cellular organelles called chloroplasts containing the chlorophyll which turns sunlight into sugars, and gives all plants their green colour. The fact that some cells in leaves of M. jalapa lose their chloroplasts and their colour is due to such a cytoplasmic factor.

Light and dark. I’d like to play At the dark end of the street (1967), sung by James Carr (1942-2001). He was a powerful and moving soul singer, and this performance of a song written by Chips Moman and Dan Penn is his masterpiece – one of the few records I think of as perfect, unimprovable.  Unfortunately Carr seemed unable to cope with his success in the late 60s, and made few further records.   For the rest of his life he engaged in a long struggle with bipolar disorder.

Coming up next: a bunch of roses.



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