16 INTKODUCTIOH". 



Most of the terms used for describing the forms of leaves are also ap- 

 plicable to those of individual petals : but the flat expanded portion of a 

 petal, corresponding to the blade of the leaf, is called its -lamina, and the 

 stalk, corresponding to the petiole, its claiv (unguis). 



§ 10. The Stamens. 



Although in a few cases the outer stamens may gradually pass into petals, 

 yet, in general, Stamens are very different in shape and aspect from leaves, 

 sepals, or petals. It is only in a theoretical point of view (not the less im- 

 portant in tlie study of the physiological economy of the plant) that they 

 can be called altei-ed leaves. 



Their usual form is a stalk called the filament, bearing at the top an an- 

 ther divided into two pouches or cells. These cells are fiUed with pollen, 

 consisting of minute grains, usually forming a yellow dust, which is scat- 

 tered, when the flower expands, from an opening in each cell, in the form of 

 a slit or a pore. When the two cells are not closely contiguous, the por- 

 tion of the anther which unites them is called the connectivum. 



The filament is often wantmg, and the anther sessile, yet still perfect ; but 

 if the anther, which is the essential part of the stamen, is wanting, or does 

 not contain any poUen, the stamen is imperfect, and is more especially said 

 to be barren, abortive, or rudimentary (see above, p. 12), according to the 

 degree to which the imperfection is carried. Imperfect stamens are often 

 termed staminodia. 



In unsymmetrical flowers, the stamens of each whorl are sometimes re- 

 duced in number below that of the petals, even to a single one, and in seve- 

 ral Natural Orders or genera they are multij)hed indefinitely.. 



The terms monandrous and polyandrous are restricted to flowers wliioh 

 have really but one stamen, or an indefinite number respectively. Where 

 the stamens are luiited into one, the flower is said to be synandrows. 

 Stamens are 



monadelphous, when united by their filaments into one cluster. This 

 cluster either forms a tube round the pistil, or, if the pistil is wanting, 

 occupies the centre of the flower. 



diadelphous, when so united into two clusters. The term is more par- 

 ticularly apphed to certain Leguminosee, in which nine stamens are united 

 by then- filaments into a tube spht open on the upper side, and a tenth, 

 placed in the sht, is free. 



triadelphous, pentadelphous, and polyadelphous, when so united into 

 three, five, or several clusters. 



syngenesious, when united by their anthers in a ring round the pistil, 

 the filaments usually remaining free. 



didynamous, when (usuaUy in a bilabiate flower) there are four stamens 

 in two pairs, those of one pair longer than those of the other. 



tetradynamous, when (in Crucifers) there are six, four of them longer 

 than the two others. 

 An Anther is 



adnate, when continuous with the filament, the anther-cells appearing 

 to lie their whole length along the upper part of the filament. 



versatile, when attached by then- back to the very point of the fila- 

 ment, so as to swing loosely. 



innate, when firmly attached to the filament, and yet not entirely ad- 

 nate. 



Antber-cella may be parallel, or diverging at a less or greater angle ; or 



