. Plant studies; an elementary botany. Botany. 364 PLANT STUDIES. any organization of carpels which appears as a single organ with one ovary is a pistil. The ovules (megasporangia) are developed within the ovary (Fig. 325) either from the carpel wall, when they are foliar, or from the stem axis which ends within the ovary, when they are cauline (see § 89). They are similar in struc- ture to those of Gymnosperms, with in- tegument and micropyle, nucellus, and emhryo-sac (megaspore), except that there are often two integuments, an outer and an inner (Fig. 326). 242. Modifications of the flower.—
. Plant studies; an elementary botany. Botany. 364 PLANT STUDIES. any organization of carpels which appears as a single organ with one ovary is a pistil. The ovules (megasporangia) are developed within the ovary (Fig. 325) either from the carpel wall, when they are foliar, or from the stem axis which ends within the ovary, when they are cauline (see § 89). They are similar in struc- ture to those of Gymnosperms, with in- tegument and micropyle, nucellus, and emhryo-sac (megaspore), except that there are often two integuments, an outer and an inner (Fig. 326). 242. Modifications of the flower.—In general, the flower may be regarded as a modified branch bearing sporophylls and usually floral leaves. Its repre- sentative among the Pteridophytes and Gymnosperms is the strobilus, which has sporophylls but not floral leaves. In Angiosperms it begins in a simple and somewhat indefi- nite way, gradually becomes more complex, until finally it appears as an elaborate and very efficient structure. The evolution of the flower has proceeded along many lines, and has resulted in great diversity of structure. These diversities are largely used in the classification of Angio- sperms, as it is supposed that near relatives are indicated by similar floral structures, as well as by other features. Some of the lines of evolution may be indicated as fol- lows : 1. From naked flowers to those with distinct calyx and corolla.—In the simplest flowers floral leaves do not appear, and the flowrer is represented only by the sporophylls. When the floral leaves first appear they are inconspicuous, scale-like bodies. In higher forms they become more promi- nent, but are still all alike. At last the floral leaves become differentiated, the outer set (calyx) remaining scale-like or Fig. 326. A diagrammatic section of an ovale of Angiosperms, showing outer integument (ai), inner integument (ii), micropyle (m), nucellus (/:). and embryo-sac or megaspore (em).—After Please note that the
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