Index Londinensis to Illustrations of Flowering Plants, Ferns and Fern Allies Being an Emended and Enlarged Edition Continued Up to the End of the Year 1920 of Pritzel's Alphabetical Register of Representations of Flowering Plants and Ferns Compiled from Botanical and Horticultural Publications of the Xviiith and Xixth Centuries; Prepared Under the Auspices of the Royal Horticultural Society of London at the Royal Botanic Gardens, Kew