NUMBER OF STAMENS.—INSERTION OF STAMENS. 253 
usually the case (jig. 536, p), or four as in Poranthera (fig. 537, p), 
or many as in the Mistletoe, or only one as in Tetratheca juncea 
(fig. 538). 
4, Valvular or Opercular.—This name is applied when the 
whole or portions of the face of the anther open like trap-doors, 
which are attached at the top and turn back asif ona hinge. In 
the Barberry (jig. 540) there are but two such valves or lids ; 
while in plants belonging to the Laurel order there are two or 
four such lids (fig. 541, v), according as the anthers have two 
or four cells. 
THE STAMENS GENERALLY, OR THE ANDR@&cIUM.—Before de- 
scribing the pollen which is contained within the anther, it will 
be better to take a general view of the stamens as regards their 
relations to one another, and to the other whorls of the flower. 
We shall consider this part of our subject under four heads, 
namely :—-1. Number ; 2. Insertion or Position; 3. Union ; 
4. Relative Length. 
1. Nwmber.—The number of stamens is subject to great 
variation, and several terms are in common use to indicate such 
modifications. In the first place, certain names are applied to 
define the number of the stamens when compared in this re- 
spect with the component parts of the floral envelopes. Thus 
when the stamens are equal in number to the sepals and petals, 
the flower is said to be isostemenous, as in the Primrose ; and if 
they are unequal, as in the Valerians (jigs. 494 and 495), the 
flower is anisostemenous. Or, when greater accuracy is required, 
in the latter case, we say diplostemenous, if the stamens are 
double the number, as in the Stonecrop ; meiostemenous, if fewer 
in number, as in the Lilac; and polystemenous, if more than 
double, as in the Rose. 
Secondly, the flower receives different names according to 
the actual number of stamens it contains, without reference to 
the number of parts in the outer whorls. This number is 
indicated by the Greek numerals prefixed to the word androus, 
which means male, in reference to the function of the stamen. 
Thus, a flower having one stamen is monandrous, two diandrous, 
three triandrous, four tetrandrous, and so on. We shall have 
to refer to these terms again when treating of the Linnzan 
system of classification, as many of the classes in that system 
are determined by the number of stamens contained in the 
flower. 
2. Insertion or Position.—When the stamens are free from 
the calyx and pistil, and arise from the thalamus below the 
latter organ, as in the Poppy (jig. 32) and Crowfoot (fig. 542), 
they are said to be hypogynous, which signifies under the female 
or pistil ; this is the normal position of the stamens. When 
the stamens are attached to the corolla, as in the Primrose 
(fig. 543), they are epipetalous. When the stamens adhere to 
the calyx more or less, so that their position becomes somewhat 
