THE FLOWER CHART 



The flower chart (Plate 2) is an attempt to express in concise graphic 

 form the general lines of the evolution of flowering plants from the an- 

 cestral ferns, and to indicate the relationships of the various groups. By 

 following two or three simple rules which will be given later, the chart 

 also serves as a key to determining the group to which a flower belongs. 



A "flower," as the term is generally understood, is made up of four 

 different sets of parts, arranged in concentric circles at the tip of a stem 

 or flower-stalk. The outer circle is composed of green, leaf-like structures 

 known as sepals or calyx. The next circle of white or colored parts con- 

 sists of petals, which form the corolla. Within this row, or sometimes 

 fastened to the petals, are the pollen-bearing organs or stamens, made up of 

 little sacks which contain the pollen and are attached to slender stalks or 

 filaments. In the center of the flower are found the pistils or a single pistil. 

 Each usually has a swollen or enlarged part at the base, the ovary, which 

 contains the ovules or young seeds, a slender stalk or style arising from the 

 ovary, and a roughened or branched end to the style, called the stigma. 



The simplest flowers occur among the families of cone-bearing trees 

 and shrubs, and among the buttercups. The flowers of the former are 

 made up of cones of pollen-bearing and of seed-bearing scales, and lack 

 both calyx and corolla. The flowers of the buttercups, on the other hand, 

 possess calyx or corolla, or both, as well as stamens and pistils, and are 

 regarded as the most primitive or the simplest flowers, among what are 

 popularly known as "flowering plants." In detail, one of these primitive 

 or simple flowers is made up of a large number of separate stamens and 

 pistils, and a variable number of separate similar petals and separate 

 similar sepals. The flower parts are arranged, as indicated above, in con- 

 centric circles on the end of the flower stalk or "receptacle" and at practi- 

 cally the same level. A simple flower of this sort may become advanced 

 or specialized by one or more of the following changes: (1) reduction in 

 number of parts, (2) union of parts among themselves or with each other, 



