e, _-androus_. Two
other terms, of same origin, designate particular cases of number (four
or six) in connection with unequal length. Namely, the stamens are

_Didynamous_, when, being only four, they form two pairs, one pair
longer than the other, as in the Trumpet Creeper, in Gerardia (Fig.
263), etc.

_Tetradynamous_, when, being only six, four of them surpass the other
two, as in the Mustard-flower and all the Cruciferous family, Fig. 235.

286. =The Filament= is a kind of stalk to the anther, commonly slender
or thread-like: it is to the anther nearly what the petiole is to the
blade of a leaf. Therefore it is not an essential part. As a leaf may be
without a stalk, so the anther may be _Sessile_, or without a filament.

[Illustration: Fig. 292. Stamen of Isopyrum, with innate anther. 293. Of
Tulip-tree, with adnate (and extrorse) anther. 294. Of Evening Primrose,
with versatile anther.]

287. =The Anther= is the essential part of the stamen. It is a sort of
case, filled with a fine powder, _the Pollen_, which serves to fertilize
the pistil, so that it may perfect seeds. The anther is said to be

_Innate_ (as in Fig. 292), when it is attached by its base to the very
apex of the filament, turning neither inward nor outward;

_Adnate_ (as in Fig. 293), when attached as it were by one face, usually
for its whole length, to the side of a continuation of the filament; and

_Versatile_ (as in Fig. 294), when fixed by or near its middle only to
the very point of the filament, so as to swing loosely, as in the Lily,
in Grasses, etc. Versatile or adnate anthers are

_Introrse_, or _Incumbent_, when facing inward, that is, toward the
centre of the flower, as in Magnolia, Water-Lily, etc.

_Extrorse_, when facing outwardly, as in the Tulip-tree.

288. Rarely does a stamen bear any resemblance to a leaf, or even to a
petal or flower-leaf. Nevertheless, the botanist's idea of a stamen is
that it answers to a leaf developed in a peculiar form and for a special
purpose. In the filament he sees the stalk of the leaf; in the anther,
the blade. The blade of a leaf consists of two similar sides; so the
anther consists of two LOBES or CELLS, one answering to the left, the
other to the right, side of the blade. The two lobes are often connected
by a prolongation of the filament, which answers to the midrib of a
leaf; this is called the CONNECTIVE. This is conspicuous in Fig. 292,
where the connective is so broad that it sepa