THE STAMKNS. 281 



perigynous (467) wlien borne on or adnate to any part of the calyx ; 

 epipetalous, when borne on the corolla, as in the greater number of 

 monopetalous floAvers ; and epigynons (469), 

 when borne on the ovary. In some cases the 

 adnation proceeds further, and the stamens are 

 inserted on, i. e. are consolidated with, the 

 style, as in the Orchis family ; then they ai-e 

 said to be gynandrous (Fig. 468). 



520. There are two cases in Avhich 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 Gei-ardia (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 femily 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 Avhat 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 stei-ile, 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. TllC Filament, although usually slender and stalk-like, assumes 

 a great variety of foi'ms : it is sometimes dilated so as to resemble a 

 petal, except by its beai'ing 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 Anllier, which is the essential part of the stamen, is usu- 

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

 two loles, or cells (jhecce), placed side by side, and connected by a 

 prolongation of the filament, called the connectiviim, or connective. 



FIG. 468. Stamens and style of a Cypripedium, united into one body or column: a^a, 

 anthers : si. a sterile stamen : s//^. the stigma. 



24* 



