. Introduction to structural and systematic botany, and vegetable physiology. Botany. THE STAMKNS. 281 perigynous (467) when borne on or adiiate to any part of the calyx ; epipetaloiis, when borne on the corolla, as in the greater number of monopetalous flowers; and epigyno^is (469), when borne on the ovary. In some cases the adnation proceeds further, and the stamens are mserted on, i. e. are consolidated with, the style, as in tlie Orchis family; then they are said to be gynandrous (Fig. 468). 520. There are two cases in which inequal- ity in the length of the filaments is expressed by a tec
. Introduction to structural and systematic botany, and vegetable physiology. Botany. THE STAMKNS. 281 perigynous (467) when borne on or adiiate to any part of the calyx ; epipetaloiis, when borne on the corolla, as in the greater number of monopetalous flowers; and epigyno^is (469), when borne on the ovary. In some cases the adnation proceeds further, and the stamens are mserted on, i. e. are consolidated with, the style, as in tlie Orchis family; then they are said to be gynandrous (Fig. 468). 520. There are two cases in which inequal- ity in the length of the filaments is expressed by a technical term. Namely, the stamens are said to be didynamous when, being only four in number, they are in pairs, and one pair is *^ longer than the other; as in Gerardia (Fig. 407), and in most flowers with a bilabiate corolla. And they are tetradynamous when, being six in number, two are shorter than the remaining four, as in Mus- tard and all that family of plants with Cruciferous flowers (Fig. 406). 521. A stamen consists of its filament and its anther (418). The filament, being a mere stalk or support of the anther, is not an essential part; it is to the anther what the petiole is to the blade of a leaf. Sometimes, therefore, it is wanting, when the anther is sessile. The anther is essential to a perfect stamen. But sometimes a stamen, or what stands in the place of one, is destitute of an anther, i. e. is sterile, as in Fig. 408; and also the upper one in Fig. 468, St., which is a sterile filament enlarged into a petal-like body. The true nature of the organ is known by its position. 522. The Filament, although usually slender and stalk-like, assumes a great variety of forms : it is sometimes dilated so as to resemble a petal, except by its bearing an anther; as in the transition states be- tween the true petals and stamens of the Water-Lily (Fig. 344). The filament is anatomically composed of a central bundle of spiral ves- sels or ducts, which represent the fibro-vascular
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