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604 Naked seeds, improperly so-called, defined as Akena or Caryopsis, 360; how distinguishable, ibid.; sometimes originate in a premature rupture of the ovarium, 360; illustrated by various examples, 361-4

Napimoga, perhaps not different from Homalium, 120

Napoleona compared with Rafflesia, 387-8

Natural orders of plants, suggestion for combining them into natural classes, 10, 109; number of, in the publications of Jussieu and De Candolle, 10; number known in the Flora of Terra Australis [in 1814], 70; [in 1849], 338

Nelson, David, plants collected by him in Van Dieraen's Land, in Cooke's Third voyage, 6

Neottia picta, conversion of the two lateral divisions of the perianthium into stamina, 501

Nepenthes, peculiarity in the seeds of, 449

Neurada prostrata, found in central Africa, 288

Nisa referred to Homalinæ, 120

Nucleus, apex of the, regarded as the point of impregnation of the ovulum, 453

Nucleus of the cell in Orchideæ, 511—4; in other Monocotyledonous and Dicotyledonous plants, 513—4

Nuytsia floribuuda, named in honour of the discoverer of that part of the coast of New Holland, to which it is nearly limited, 308

Nymphæaceæ, genera belonging to, 451; explanation of the structure of the seed in, 451-2; arrangement of ovula in the carpels of, 377 note, 555

Olacinæ, observations on the order and its affinity to Santalaceæ; and on the species found in the vicinity of the Congo, 136

Olax, observations on the genus and its affinities, 44; on species found in the vicinity of the Congo, 136

Onagrariæ, molecules in the grains of pollen of various species of, 467

Opercularia, undoubtedly referrible to Rubiaceæ, 36

Ophrys, monstrosity of, described and figured by M. His, 501; impregnation in, generally effected without the aid of insects, 538

Ophrys apifera, mucous tubes inserted into the aperture of ovulum in, 540 note; cellular thread of ovulum in, 547

Ophioglosseæ, affinity of Triplosporite to, 588

Orange of the banks of the Congo, probably of Asiatic origin, 156

Orchideæ, observations on the order and on its distribution in Terra Australis, 48; structure of the flower approximated to the type of Monocotyledons, 48; compared with that of Scitamineæ, 49; modifications of antheræ of superior importance to those of labellum, 86; their simple or acotyledonous embryo, 414-5; observations on the organs and mode of fecundation in, 487—543; supplementary observations on, 545—551; opinions of various writers on, 490—8; origin of the stigmata and placenta; in, 560—2; cellular thread suspending the embryo in, 569; on the relation of the lateral stamina, 499; believed to be placed opposite to the lateral divisions of the inner series of perianthium, ibid.; auriculæ of the column in, 500; inner series of perianthium converted into stamina in, 501; composition of the stigma and ovarium in, 501—4; made up of three component parts, 502; Mr. Francis Bauer's views controverted, 502-3; functions of the different lobes of stigma, 503; relative position of stamina and stigmata, 504; development of unimpregnated ovulum, 504-5; conducting surfaces of the ovarium, 505-6; mode of impregnation in, 506—510; production and course of pollen tubes, 507—510; distinctive characters of the tubes, 507; generally very numerous and forming a cord dividing into six portions, passing along the conducting surfaces, 508; tubes separating and