. Introduction to structural and systematic botany, and vegetable physiology. Botany. 298 THE coat: this appears as a circular ring around the base of the forming nucleus, which gradually becomes cup-shaped, and at length covers it like a sac, remaining open, however, at the summit. Tliis orifice is called the Foramen, or MiCROPYLE. In far the greater number of cases, a second envelope is formed out- side of the first, beginning in the same way, though always later than the inner one, which, however, it eventually over- takes and encloses. Mirbel named the exterior coat of the ovule t
. Introduction to structural and systematic botany, and vegetable physiology. Botany. 298 THE coat: this appears as a circular ring around the base of the forming nucleus, which gradually becomes cup-shaped, and at length covers it like a sac, remaining open, however, at the summit. Tliis orifice is called the Foramen, or MiCROPYLE. In far the greater number of cases, a second envelope is formed out- side of the first, beginning in the same way, though always later than the inner one, which, however, it eventually over- takes and encloses. Mirbel named the exterior coat of the ovule the Primine, and the in- terior the Secundine, — names which are attended with the objec- tion that the secundine or inner coat is actually older than the primine or exterior coat. Both sacs are open at the apex, and the summit of the nucleus points directly towards the apertures. The orifice or foramen of the primine or exterior integument is called the ExosTOSlE (or outer orifice); that of the interior or secundine, the Endostome (or inner orifice). The coats of the ovule and the nucleus are distinct and unconnected, except at the base, or point of attachment to the funiculus, where they are all confluent: this point of union receives the name of the Chalaza (Fig. 521, d). Through the funiculus and chalaza the ovule derives its nourish- ment from the placenta; through the opening at the summit, the nucleus receives the tubular prolongation of the pollen, which incites the formation of the embryo. 565. Ovules occur under four principal forms, viz. the orthotro- pous or straight, the campylotropous or curved, the amphitropous or half-inverted, and the anatropous or inverted. The simplest, al- though the least common of these, is 5C6. The Ol'thotropous Ovule, also termed atropom (viz. not turned). It is the form which this organ assumes in the Buckwheat family (Fig. 518), and several others, and is likewise shown in Fig. 520, 526, and a longitudinal section of it in Fig. 521. H
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