Oncidium, 332.
Oncobyrsa, 24.
Onion, 312.
Onobrychis, 472, 473.
Ononis, 471.
Onopordon, 570.
Ooblastema-filaments, 82.
Oocystis, 51.
Oogamous fertilisation, 13.
Oogonium, 13.
Oomycetes, 95, 96, 100.
Oophyte, 181.
Oosphere, 13, 248.
Oospore, 14.
Operculum, 193.
Ophiocytium, 51.
Ophioglossaceæ, 209, 210.
Ophioglossum, 210, 211, 238.
Ophiopogon, 320.
Ophrydeæ, 331.
Ophrys, 332, 333.
Opium-poppy, 395.
Oplismenus, 295.
Opuntia, 375, 377.
Orange, 438.
Orchid, diagram of flower, 329.
Orchidaceæ, 5, 238, 328.
Orchideæ, 277.
A Handbook of Systematic Botany · The Wunder Library — complete classics, free to read, with narration.