PLANT ORGANS AND ORGANISMS 



189 



some Aceracea, these being in two circles. In Malvacea, Umbelliferce 

 and other Apopetalous families as well as many Sympetalae, the 

 number five is typical. But in Scropkulariacece, 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. 93^4). 



Perigynous, when inserted on the calyx or corolla above the base of 

 and lateral to the pistil (see Fig. 93$). 



Epigynous, when inserted above the ovary (see Fig. 936"). 



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. 



Triadelphous, with filaments united into three sets. Example: 

 St. John's Wort. 



