INTROBUCTION XXV 



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

 of the preceding whorl, the p'-'tals 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. 



^^'here the floral leaves in each whorl are similar in size and 

 shape the flower can be divided symmetrcally in several direc- 

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

 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 iiionosynimetric. 

 Occasionally it is asviiuneiric, 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 inscriion 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 pcrigynous 

 inserLiLin. 



Flower of Buttercup 

 in section, showing 

 hypig) nous insertion. 



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

 and stamens are Iiypogj-iwus (Greek htipo, under, gu?ie, a woman), 

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

 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 ca>5'x 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 z.-a& the ovary formed b}' the carpels inferior, the petals 

 and stamens being still perigynous. If, la,stly, as in Composita 

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

 stamens on to the top of the ovary, the cah'x is superior, the ovar\- 

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

 When the petals and stamens are perigynous or epigynous the 



