theory of descent but like Sprengel had a teleological approach and explained the mechanisms of flowers by the intervention of a "psychovitalistic intelligence". Delpino classified flowers on the basis of the pollinators they attracted, and coined many of the terms still in use such as pollination syndrome and ornithophily. There was an enormous increase in knowledge during this period. In 1874, Asa Gray paid tribute to Darwin's work on orchids for explaining "all these and other extraordinary structures, as well as of the arrangement of blossoms in general, and even the very meaning and need of sexual propagation". He credited Darwin with establishing the understanding that "Nature abhors close fertilization". By the end of the 19th century, there were so many uncritical and unproven speculations about floral mechanisms that floral ecology became discredited. In the 1920s, it was revived with further developments in detailed analyses of insects' senses, led by researchers Frederic Clements, Karl von Frisch and others. Their experiments resulted in new information, including the discovery that some insects have ultraviolet vision, and findings involving bee learning and communication. Modern floral ecology has been reinvigorated by its relevance for evolutionary studies. Further research by Darwin Darwin had "found the study of orchids eminently useful in showing me how nearly all parts of the flower are coadapted for fertilisation by insects, & therefore the result of n. selection,—even most trifling details of structure". His own interest in orchids and in fertilisation of plants by insects continued. Darwin had been given the use of a hot-house at The Rookery on the other side of the village, and at the end of 1862 he was persuaded by this neighbour's helpful gardener to have his own built at Down House as an extension to the existing cold lean-to greenhouse. The gardener drew up plans, and Darwin investigated stoves and ventilation devices. When it was completed in February 1863 he asked Hooker for some plants from Kew Gardens, writing "I long to stock it, just like a school-boy", and sent his butler with a cart. When over 160 different plants were delivered, Darwin made apologetic remarks about depleting the national collection. He told Hooker "You cannot imagine what pleasure your plants give me ... Henrietta & I go & gloat over them." Darwin's life was changed by having a warm hothouse to spend time in before his walk round the Sandwalk, and in the