The Downe Valley is a dry chalk valley to the west of Down House, its steep sides with a thin soil supporting chalk grassland while the tops of the slopes are covered with acid soil derived from clay-with-flints and supporting patches of semi-natural ancient woodland. In ‘Life and letters of Charles Darwin’ (1887), Darwin’s son, Francis, wrote how the charm of this simple little valley helped Charles Darwin settle at Down and described it as:
"A quiet little valley losing itself in the upland country towards the edge of the Westerham hill, with hazel coppice and larch wood, the remnants of what was once a large wood, stretching away to the Westerham road."
Darwin carried out many studies here and the family gave special names to different areas in the valley. These included ‘The Big Woods’ where Darwin observed cowslips and primroses and collected seeds of the hybrids between them (false oxslips) which he took home and planted in his kitchen garden. An entry in his notebook for 27th April 1862 noted how the following spring they grew up ‘well true’. Details of Darwin’s work on primroses, orchids and hybrids between them can be found in: ‘The different forms of flowers on plants of the same species’. (1877) at www.darwin-online.org.uk. It was also here that Darwin and his son, George, observed how common spotted orchids were pollinated by empid flies (see 'Notes on the Fertilization of Orchids’, Annals and Magazine of Natural History, 4th series, iv. 1869, pp. 141-159).
To reach the ‘Big Woods’ the Darwins had to walk from their kitchen garden, or from the Sandwalk, westwards down a sloping field known as Great Pucklands (or Stony Field) and through an ancient shaw (belt of woodland). Darwin noticed how some spindle bushes in the shaw generally produced large amounts of fruit, some very little or none at all, and some consistently produced a moderate amount. This led him to mark the bushes and return to observe the flower structure in the spring of 1864. He found that spindle had 3 different flower types: some were functionally male, some female and those with moderate amounts of fruit were hermaphrodite. More details of his observations can be seen in,
"Different forms of flowers on plants of the same species." (1877)
Below the shaw, a walk along the side of the Downe Valley was called ‘The Terrace’ by the family. In , ‘Emma Darwin: A century of family letters’ (1904) Charles’ daughter, Henrietta, described how,
"The terrace was sheltered from the north-east by a rough shaw of beeches and an undergrowth of sloes, traveller's joy, service-trees and hawthorn, and this bank was particularly gay with the flowers that love a chalk soil - little yellow rock-rose, milkwort, orchises, ladies' fingers, hare-bells, coronilla, scabious and gentian. There were rabbits in the shaw, and Polly, the little fox-terrier, loved this walk too. My father would pace to and fro, and my mother would sometimes sit on the dry chalky bank waiting for him, and be pulled by him up the little steep pitch on the way home."
A walk north along ‘The Terrace’, led to Green Hill where, in 1863, Darwin observed hairy violet noting,
"1 April 1863 I watched 1000’ of wild flowers; at last saw …….one Hive-Bee visiting & sucking several. Marked 6 flowers of V. hirsute [hairy violet] with black thread, which I saw sucked - Of these 6, 2 set fine pods."
This was one of many observations he made concerning cross-pollination and the viability of seeds produced compared to the viability of seeds resulting from self-pollination.