A^WGIOSPERMS. ^01 



Viola only one of the perianth-leaves forms a hollow spur, into which the append- 

 ages of two stamens are prolonged and secrete the nectar. The cup-shaped stalked 

 petals of Helleborus and the slipper-shaped petals of Nigella excrete at the bottom 

 of their cavity the nectar which gathers there. 



The Oz'uk of Angiosperms usually consists of a clearly developed, sometimes 

 even very long stalk or Funiculus (as in Opuntia and Plumbaginese) — which, how- 

 ever, is sometimes entirely wanting, as in Grasses — and one or two integuments 

 which enclose the nucleus. The ovules of most gamopetalous Dicotyledons have 

 one, those of almost all Monocotyledons two integuments ; a third envelope, the 

 Aril, is frequently formed subsequently (as in INIyristica, Euonymus, Asphoddus 

 luka, Aloe subiuberciilata, &c. When the ovule is the terminal structure of the 

 floral axis, and has a short funiculus, it is orthotropous, as in Piperaceae and Poly- 

 gonacese; the campylotropous form, i. e. where the nucleus together with its 

 integuments is itself curved, is comparatively rare, but occurs in Grasses, Fluviales, 

 Caryophyllese, &c. The usual form of the ovule of Angiosperms is the anatro- 

 pous; the nucleus together with its integuments is inverted, so that the micropyle 

 faces the point of origin of the funiculus from the placenta (Figs. 351 E, 352, 

 pp. 489, 490) ; in this case the funiculus runs up the side of the ovule, coalesces with 

 it, and is termed the Raphe. The micropyle is frequently, especially in Monocotyle- 

 dons, formed by the inner integument only of the nucleus ; but sometimes, especially 

 among Dicotyledons, the outer integument grows also above the opening of the inner 

 one, and the channel of the micropyle is then formed at its outer part (the Exostome) 

 of the outer, at its inner part (the Endosio77ie) of the inner integument. When there 

 are two or three integuments, the innermost (the Primine of IMirbel) is always 

 formed first, then the outer one (the Secundine), and finally, usually at a much later 

 period, the Aril ; the order of development is therefore basipetal in reference to the 

 axis of the ovule. The transverse zone from which the single or the two true integu- 

 ments spring, is termed the Chalaza (more correctly the base of the ovule). 



The integuments are usually only a few layers of cells in thickness, and have 

 the appearance, especially when they enclose a large nucleus, of thin membranes 

 (Fig. 351, E). But when only one integument is developed, the nucleus usually 

 remains very small, while the integument becomes thick and solid, extending far 

 beyond the nucleus, and forming, before fertilisation, the principal mass of the 

 ovule, as in Hippuris (Fig. 330, p. 470), UmbeUiferae (Fig. 352, p. 490), and Com- 

 positae (Fig. 362, p. 497)- 



There is still much doubt about the history of development of the separate 

 parts of the ovule; the following may be stated as certain or at least probable. 

 In the formation of the erect orthotropous ovule the apex of the floral axis rises 

 within the ovary as a roundish or conical ovoid protuberance which forms the 

 nucleus ; an annular wall grows up first, and finally envelopes the nucleus and 

 extends beyond it as an integument. If a second outer integument is formed in 

 addition, this arises in a similar manner, and grows up around the first (as in 

 Piperacese, Polygonaceae, &c.). The anatropous ovule may be at first a straight or 

 slightly curved projection of tissue (as in Fig. 366, /), but immediately becomes 

 evidently curved at the spot where the first or the single integument springs from it 

 (Fig. 366, //, ///, IV) ; the apical part enclosed by the integument then forms the 



