FLOWER CHART xiii 



as indicated by placing the symbol above that for the corolla. Practically 

 every flower with a united corolla possesses a united calyx and stamens 

 fastened to the corolla tube. When there is a change in the position of 

 the corolla from the end of the flower-stalk to the top of the ovary, the 

 calyx-lobes and stamens are found at the same level. When the corolla 

 becomes irregular in shape, the calyx usually shows irregularity also. The 

 number characteristic of any flower is usually the same for calyx and 

 corolla, and frequently for the stamens. Thus, in studying any particular 

 flower, the number, position and character of the petals is of more im- 

 portance than variations in other parts, except the pistil. As noted above, 

 the great change in the latter is the union of simple pistils into a compound 

 ovary and the reduction in the number of cells. 



To sum up, the changes which occur in the evolution of the higher or 

 more specialized forms of flowers from the lower or simpler ones, in order 

 of their importance, are (1) union of pistils, (2) elevation of corolla, 

 (3) union of corolla and (4) irregularity of corolla. The cross lines on 

 the chart indicate at what points in the three main lines of development 

 these different changes occur. The buttercup-aster line of development 

 shows all four of the possible changes and thus asters are considered the 

 most highly developed group of the entire plant kingdom. The other two 

 lines — from buttercups to orchids, and from buttercups to mints — have 

 each emphasized one of the four possible changes and have as yet made 

 regular use of but three. In the buttercup-orchid line there is no union 

 of petals except in occasional instances, while in the buttercup-mint line 

 there is no elevation of the petals except in rare cases. Both of these 

 lines, however, possess at the upper ends examples of the most irregular 

 flowers known. 



Taking up the steps of advance as they occur in order in the three 

 lines of evolution, it will be noticed that the arrowhead family, nearest 

 the buttercups in the buttercup-orchid line, are merely buttercups with 

 flower parts in threes. They show no distinct step of advance, but like 

 other members of this line, often called monocotyledons, have parallel- 

 veined leaves and a single seed-leaf. The number three is thereafter char- 

 acteristic of all the families of this line of development, and the other 

 changes are additional to it. For instance, the lilies show an advance over 

 the arrowheads in having reduced the pistils to three and having united 

 them into a compound ovary with three cells. In most lilies, the sepals 

 have become brightly colored like the petals, and this similarity is there- 

 after characteristic of the higher types in the same line of advance. The 

 irises have gone one step farther than the lilies by raising the colored 

 perianth of petals and sepals upon the ovary, making the latter inferior. 



