44 THE EVOLUTION OF PLANTS 



and an inner, the corolla, commonly composed of 

 brightly-coloured leaves, the petals. This is 

 the case in most of our familiar flowers, es- 

 pecially those of the plants which have two seed- 

 leaves (Dicotyledons). Either the whole per- 

 ianth, or the corolla, as the case may be, is the 

 conspicuous part, in cases where the flower is 

 attractive to insects by its colour. 



Within the perianth come the stamens, ranged 

 in a single circle as in the Primrose, or in a double 

 circle as in the Geranium, or numerous and 

 spirally disposed as in the Buttercup. Lastly, 

 in the middle of the whole flower, stands the 

 pistil, consisting of one or more carpels, either 

 free or united in various ways, and containing 

 the ovules or young seeds. 



This typical structure is common to Dico- 

 tyledons and Monocotyledons; it is subject to 

 every degree of variation, in the number of the 

 organs and in their freedom from, or union to, 

 one another. Thus in the Buttercup all parts 

 of the flower are free and separate; in the Straw- 

 berry and many other plants of the Rose family, 

 all parts are free, except the calyx, in which the 

 sepals are partly joined together. In a Prim- 

 rose the petals of the corolla are also united to 

 form a tube, and the stamens are joined to the 

 corolla. The stamens in most flowers are sepa- 

 rate from one another, but in the Mallow they are 



