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 system of the leaf, 

 in the same state as in the petiole, enveloped by parenchyma ; the 

 outer stratum of which forms a delicate epidermis. 



523. The Anther, which is the essential part of the stamen, is usu- 

 ally borne on the apex of the filament ; and commonly consists of 

 two lohes, or cells (thecce), jjlaced side by side, and connected by a 

 prolongation of the ^lament, called the connectivum, or connective. 



FIO. 468. Stamens and style of a Cypripedium, united into one body or column ; a, o, 

 antliers : si.2. sterile stamen : stig. the stigma. 



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