. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. OVULES 357 Composite). This last condition is often characteristic of some of the most advanced types of Flowering Plants. The ovules of Angiosperms (Fig. 206), which in their general construction are hke those of Gymnosperms, usually possess two integuments (inner, , and outer, ). A single one is the rule amongst the gamopetalous Dicotyle- dons (Sympetalse) and a few polypetalous families { UmbeUiferffi, Salica- ). In these latter, however, the single in- tegument is generally re- la
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. OVULES 357 Composite). This last condition is often characteristic of some of the most advanced types of Flowering Plants. The ovules of Angiosperms (Fig. 206), which in their general construction are hke those of Gymnosperms, usually possess two integuments (inner, , and outer, ). A single one is the rule amongst the gamopetalous Dicotyle- dons (Sympetalse) and a few polypetalous families { UmbeUiferffi, Salica- ). In these latter, however, the single in- tegument is generally re- latively robust, a fact which suggests its possible origin from the fusion of two ; a partial union of this character is, indeed, seen in some members of the Ranunculaceffi.^ The nucellus («.), with very few exceptions { Bog Myrtle, Myrica), is only clearly separated from the integument at the apex, where it forms a cap of tissue extending between the large mega- spore (embryo sac, , see p. 365) and the micro- pyle {m.). The part of the nucellus in contact with the integument can often be distinguished from the latter, in sections of the ovule, by the dense contents of its cells, ^^'hich form a nutritive layer around the developing embryo sac. By far the commonest tj'pe of ovule is the anatropous one (Figs. 206 and 207, C), in which the main body of the ovule is. Fig. 20G.—Diagrammatic longitudinal section through an anatropous ovule, greatly magnified. a., antipodal cells ; Ch., chalaza ; e., egg ; , embryo sac; /., funicle ; , inner integument; m., micropyle ; «., nucellus ; , outer integument; ^., polarnuclei; r., raphe; s., syner- gida;; , vascular bundle of raphe. ' In a few Rosacea; [ Geiiiii) there is only a single integument due to failure of the inner one to Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
