THE PISTIL. 137 



pairs of different lengths, they are said to be didynamous 

 (Fig. 60) ; if six in number, four long and two short, they 

 are tetrad ynamous (Fig. 28) ; and, finally, if the stamens 

 are hidden in the tube of a gamopetalous corolla they are 

 said to be included, but if they protrude beyond the tube 

 they are exserted (Fig. 177). 



215. The Pistil. This is the name given to the 

 central organ of the flower. It is sometimes also called the 

 gyncecium. As in the case of the stamens, the structure 

 of the pistil must be regarded as a modification of the 

 structure of leaves generally. The pistil may be formed 

 by the folding of a single carpellary leaf, as in the Bean 

 (Fig. 188), in which case it is simple; or it may consist 

 of a number of carpels, either entirely separate from each 

 other or united together 



in various ways, in which 



case it is compound. By 



some botanists, however, 



the term compound is 



restricted to the case of Fig. IBS. 



united carpels. If the carpels are entirely distinct, as in 



Buttercup, the pistil is apocarpous ; if they are united in 



any degree, it is syncarpous. A pistil of one carpel is 



monocarpellary ; of two, dicarpellary ; and so on, to 



poly carpellary. 



216. The terms inferior and superior, as applied to the 

 pistil, describe its situation upon the axis relative to 

 that of the calyx, corolla, and stamens. It will be 

 remembered that the end of the peduncle is usually 

 enlarged, forming what is called the torus or receptacle. 

 Usually the receptacle is a little higher in the centre 



Fig. 188, Legume of the Bean. 



