1870s he had several more hothouses built. The children later remembered this routine and the gardeners attending to Darwin's experimental plants, as well as the way that Darwin used simple equipment for his experiments, dissecting and measuring plants and seeds. A chance observation "thoroughly aroused" Darwin's attention to a surprising decrease in vigour of the offspring of Linaria vulgaris following only one instance of self-fertilisation, and after eleven years of experimental work he published The Effects of Cross and Self Fertilisation in the Vegetable Kingdom in 1876 as "a complement to the 'Fertilisation of Orchids,' because it shows how important are the results of cross-fertilisation which are ensured by the mechanisms described in that book." He told a friend "I cannot endure doing nothing", and resumed his work on orchids, assisted in his research by his son Francis Darwin. He corresponded about orchids with Fritz Müller, and almost completely rewrote the book with a considerable amount of new material, much of which was contributed by Müller. The revised edition was published in 1877. Francis Darwin described it as characteristic that his father delighted in the observations that preceded the publication of Fertilisation of Orchids, not the applause which followed it. He quoted one of his father's last letters about orchids, written in 1880: Commemoration of Darwin's work on orchids Kent Wildlife Trust manages Downe Bank, which is near Down House and was a favourite place of the Darwin family, who called it 'Orchis Bank' because of the many wild orchids which grew there. It is now part of the 'Downe Bank and High Elms' Site of Special Scientific Interest. Darwin's observations of local orchids and their insect pollinators gave him the evidence for co-evolution which provided the basis for the Fertilisation of Orchids." Experts have identified "Orchis Bank" as the species-rich setting encapsulated in the closing paragraph of On the Origin of Species, in which Darwin wrote: Darwin's home and its surroundings, including specifically "Orchis Bank", have been called his landscape laboratory, and together were nominated in January 2009 for designation as a World Heritage Site. The bid was made by a partnership led by the London Borough of Bromley, which now includes Downe. It was included in the 39 proposed properties, but was not in the 21 new sites selected for the list. The influence of Darwin's work was commemorated in the Smithsonian Institution's 15th Annual Orchid Show, Orchids