PLANT ORGANS AND ORGANISMS 
some Aceracea, these being in two circles. In Malvacece , Umbelliferce 
and other Apopetalous families as well as many Sympetalae, the 
number five is typical. But in Scrophulariacece , while five are devel¬ 
oped and fertile in Verbascum, four with a fifth staminode (Sterile 
stamen) are found in the allied genus Celsia. In Pentstemon there 
are four didynamous fertile stamens and an equally long staminode. 
In Scrophularia the fifth staminode is reduced to a petaloid flap in 
the posterior part of the flower. In Linaria this exists only as a 
small knob at the base of the back part of the corolla and there 
secretes nectar. In most Scrophulariacece the fifth stamen is entirely 
absent and the four stamens left are didynamous; but in 
Calceolaria two of these are rudimentary and thread-like, the 
other two alone being well-developed and fertile. In Veronica 
three stamens are entirely absorbed and two only are left as 
fertile representatives. 
Insertion of Stamens. —As to insertion the stamens may be: 
Hypogynous, when inserted upon the receptacle below the base of 
the pistil (see Fig. 93 A). 
Perigynous , when inserted on the calyx or corolla above the base of 
and lateral to the pistil (see Fig. 93B). 
Epigynous, when inserted above the ovary (see Fig. 93C). 
Gynandrous, when inserted upon the pistil, as in Orchids and Aris- 
tolochia. 
Proportions of the Stamens. —The stamens may be of equal length; 
unequal, or of different length. 
Didynamous, when there are two pairs, one longer than the other. 
Example: Snapdragon. 
Tetradynamous, three pairs, two of the same length, the third 
shorter. Example: Mustard. 
Connation of Stamens. —Terms denoting connection between sta¬ 
mens are: 
Monadelphous (in one brotherhood), coalescence of the filaments 
into a tube. Example: Lobelia. 
Diadelphous (in two brotherhoods), coalescence into two sets. 
Example: Glycyrrhiza y 
Triadelphous, with filaments united into three sets. Example: 
St. John’s Wort. 
