INTRODUCTION XXV 



As a rule, the leaves of each whorl are alternate with those 

 of the preceding whorl, the petals being opposite the spaces 

 between the sepals and the outer row of stamens opposite the 

 spaces between the petals. The Primrose and its allies form a 

 marked exception to this rule in that its stamens are opposite to, 

 or stand in front of, its petals. 



Where the floral leaves in each whorl are similar in size and 

 shape the flower can be divided symmetr.cally in several direc- 

 tions, as in the Buttercup; and it is then called polysymmetric. 

 Where from differences in the form of the leaves it can only be so 

 divided in one direction, as in the Pea, the flower is monosymmetric. 

 Occasionally it is asymmetric, or not symmetrically divisible by 

 any plane, as in Valerian. 



The Receptacle is a very important structure in the classifica- 

 tion of flowering plants, as upon it what is called the insertion of 

 the floral leaves depends. Thus if sepals, petals, stamens, and 

 carpels spring one beneath the other from a more or less conical 



Flower of Cow-pars- 

 nip, showing epi- 

 gynous insertion. 



Flower of Bramble, 

 showing perigynous 

 insertion. 



Flower of Buttercup 

 in section, showing 

 hy pig) nous i 



receptacle, as in the Buttercup, the calyx is inferior, the corolla 

 and stamens are hypogynous (Greek hupo, under, gune, a woman), 

 the carpels are superior, and the flower as a whole is called thalami- 

 floral. If, as "in the Bramble or the Strawberry, the calyx, corolla, 

 and stamens are carried out from under the carpels by a horizontal 

 disk-like extension of the receptacle, the calyx is still inferior and 

 the carpels superior, but the petals and stamens are termed 

 perigynous. So, too, if, as in the Plum or the Rose, the sepals, 

 petals, and stamens are carried up on a tube-like expansion of 

 the receptacle which does not adhere to the sides of the carpels. 

 If, as in the Apple, the Pear, and the Hawthorn, this receptacular 

 tube does adhere to the sides of the carpels, the calyx becomes 

 superior and the ovary formed by the carpels inferior, the petals 4 

 and stamens being still perigynous. If, lastly, as in Compositor 

 and Umbellijeroz, this adherent tube carries the sepals, petals, and 

 stamens on to the top of the ovary, the calyx is superior, the ovary 

 inferior, and the petals and stamens epigynous (Greek epi, upon). 

 When the petals and stamens are perigynous or epigynous the 



