On the flora of Australia : its origin, affinities, and distribution : being an introductory essay to the flora of Tasmania - Hooker, Joseph Dalton, 1817 -1911 (Lovell Reeve, 1859)

On the relation of phyllotaxis to mechanical laws - Church, A. H. (Arthur Harry), 1865 -1937 (Williams & Norgate, 1904)

On Welwitschia : a new genus of Gnetaceae - Hooker, Joseph Dalton, 1817 -1911 (s.n, 1864)

Opera e periodicis collata - Vries, Hugo de, 1848 -1935 (A. Oosthoek, 1918)

Opuscoli scientifici d'entomologia, di fisica e d'agricoltura - Termeyer, Ramón María, 1737 -1814 (Nella Stamperia del Giornale italico di Carlo Dova, contrada S. Rafaello, num. 998, 1807)

Opuscules de botanique - Clos, Dominique, 1821 -1908 (1859)

The Orchadian - Australasian Native Orchid Society (The Society, 1964)

The Orchadian - Australasian Native Orchid Society (The Society, 1965)

The Orchadian - Australasian Native Orchid Society (The Society, 1968)

The Orchadian - Australasian Native Orchid Society (The Society, 1967)

The Orchadian - Australasian Native Orchid Society (The Society, 1972)

The Orchadian - Australasian Native Orchid Society (The Society, 1977)

The Orchadian - Australasian Native Orchid Society (The Society, 1973)

The Orchadian - Australasian Native Orchid Society (The Society, 1974)

The Orchadian - Australasian Native Orchid Society (The Society, 1963)

The Orchadian - Australasian Native Orchid Society (The Society, 1980)

The Orchadian - Australasian Native Orchid Society (The Society, 1979)

The Orchadian - Australasian Native Orchid Society (The Society, 1981)

The Orchadian - Australasian Native Orchid Society (The Society, 1982)

The Orchadian - Australasian Native Orchid Society (The Society, 1983)

The Orchadian - Australasian Native Orchid Society (The Society, 1985)

The Orchadian - Australasian Native Orchid Society (The Society, 1986)

The Orchadian - Australasian Native Orchid Society (The Society, 1989)

The Orchadian - Australasian Native Orchid Society (The Society, 1988)

The Orchadian - Australasian Native Orchid Society (The Society, 1987)

The Orchadian - Australasian Native Orchid Society (The Society, 1991)

The Orchadian - Australasian Native Orchid Society (The Society, 1998)

The Orchadian - Australasian Native Orchid Society (The Society, 1997)

The Orchadian - Australasian Native Orchid Society (The Society, 1996)

The Orchadian - Australasian Native Orchid Society (The Society, 1999)

The Orchadian - Australasian Native Orchid Society (The Society, 2000)

The Orchadian - Australasian Native Orchid Society (The Society, 2001)

The Orchadian - Australasian Native Orchid Society (The Society, 2003)

The Orchadian - Australasian Native Orchid Society (The Society, 2004)

The Orchadian - Australasian Native Orchid Society (The Society, 2005)

The Orchadian - Australasian Native Orchid Society (The Society, 2007)

The Orchadian - Australasian Native Orchid Society (The Society, 2008)

The Orchadian - Australasian Native Orchid Society (The Society, 2017)

Orchard & garden book, 1944 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Company, 1944)

Orchard & garden book, 1945 - Roeding, George Christian, 1868 -1928 (California Nursery Company, 1945)

Orchard & garden book, 1946 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Company, 1946)

Orchard & garden book, 1947 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Company, 1947)

Orchard and farm (Calkins Newspaper Syndicate, 1898)

Orchard and garden book : 1865-1950, 85th year - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Seed Company, 1950)

Orchard and garden book, 1937 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Company, 1936)

The Orchid review (Orchid Review ltd.], 1894)

The Orchid review (Orchid Review ltd.], 1912)

The Orchid review (Orchid Review ltd.], 1914)

Orchidacées - Hallé, Nicolas (1977)

Les orchidées exotiques et leur culture en Europe - Cogniaux, Alfred, 1841 -1916 (l'Auteur, 1894)

Oréades - Instituto de Ciências Biológicas da UFMG. Departamento de Botânica. (Departamento de Botânica, U.F.M.G, 1970)

Oréades - Instituto de Ciências Biológicas da UFMG. Departamento de Botânica. (Departamento de Botânica, U.F.M.G, 1971)

Organographie der Pflanzen, insbesondere der Archegoniaten und Samenpflanzen - Goebel, K. (Karl), 1855 -1932 (G. Fischer, 1898)

Organographie der Pflanzen, insbesondere der Archegoniaten und Samenpflanzen - Goebel, K. (Karl), 1855 -1932 (G. Fischer, 1913)

Organographie vegetale ; ou, Description raisonnee des organes des plantes, pour servir de suite et de developpement a la theorie elementaire de la botanique, et d'introduction a la physiologie vegetale et a la description des familles, avec 60 planches en taille-douce - Candolle, Augustin Pyramus de, 1778 -1841 (Chez Deterville, libraire, rue Hautefeuille, no.8, 1827)

Organography of plants, especially of the Archegoniata and Spermaphyta - Balfour, Isaac Bayley, 1853 -1922 (Clarendon press, 1900)

Organography of plants, especially of the archegoniatae and spermaphyta - Goebel, K. (Karl), 1855 -1932 (Clar. Press, 1900)

Organologisches, systematisches und Arten-Register zu den Tafeln des Handbuch's der botanischen Terminologie - Bischoff, Gottlieb Wilhelm, 1797 -1854 (J.L. Schrag, 1849)

The origin of a land flora : a theory based upon the facts of alternation - Bower, F. O. (Frederick Orpen), 1855 -1948 (Macmillan, 1908)

The origin of a land flora : a theory based upon the facts of alternation - Bower, F. O. (Frederick Orpen), 1855 -1948 (Macmillan and co., limited, 1908)

The origin of a land flora, a theory based upon the facts of alternation - Bower, F. O. (Frederick Orpen), 1855 -1948 (Macmillan and Co., Ltd, 1908)

The origin of floral structures through insect and other agencies - Henslow, George, 1835 -1925 (D. Appleton, 1888)

The origin of floral structures through insect and other agencies - Henslow, George, 1835 -1925 (D. Appleton and Co, 1888)

The origin of floral structures through insect and other agencies - Henslow, George, 1835 -1925 (K. Paul, Trench, Trübnerco, 1888)

The origin of floral structures through insects and other agencies - Henslow, George, 1835 -1925 (D. Appleton and company, 1888)

Ornamental and fruit tree catalogue : 1926 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (Leonard Coates Nurseries, 1926)

Ornamental and fruit trees and shrubs. a guide to Southern horticulture ... 1918 catalog - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (Royal Palm Nurseries, 1918)

Ornamental and fruit trees : illustrated descriptive catalog 1921-22 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Co, 1921)

Ornamental and fruit trees : price list - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Co, 1921)

Ornamental gardening in Florida - Simpson, Charles Torrey, 1846 -1932 (The author, 1916)

Ornamental nursery stock, broad leaved evergreen trees and plants, deciduous trees and shrubs, conifers, roses, bulbs, perennial and Alpine plants - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (Beverly Hills Nurseries, 1929)

Ornamental plants for low-elevation desert areas of southern California - Mathias, Mildred Esther, 1906 - (California Agricultural Experiment Station, 1955)

Ornamental shrubs and trees fruit trees shrub and tree seed - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (Germain, 1934)

Ornamental trees and plants - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (California Nursery Company, 1908)

Ornamental trees, and shrubs, vines, hedges, perennials - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (East Lawn Nursery, 1924)

The ornamental trees of Hawaii - Rock, Joseph F. (Joseph Francis), 1884 -1962 (1917)

Ornamental trees, shrubs, hedges, roses, bedding plants [catalog] - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (East Lawn Nursery, 1927)

Ornamental trees, vines & shrubs : temporary price list, January 1940 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (Del Amo Nurseries, 1940)

Ornamental trees, vines and shrubs : descriptive price list, February 15, 1938 - Henry G. Gilbert Nursery; Seed Trade Catalog Collection. (Del Amo Nurseries, 1938)

Ornamentals for low-elevation desert areas of southern California - Mathias, Mildred Esther, 1906 - (Division of Agricultural Sciences, University of California, 1961)

Ornamentals, fruit trees, roses : 1921-1922 - Roeding, George Christian, 1868 -1928 (California Nursery Co, 1921)

Ornamentals, fruit trees, roses : 1922-1923 - Roeding, George Christian, 1868 -1928 (California Nursery Co, 1922)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1903)