FLOWERS, THEIR STRUCTURE AND KINDS 157 



of all the seed plants. They are thus believed to represent the 

 highest stage of evolution in plants. The buttercup flower is 

 much more simple in its structure, for all the parts are separate 

 and distinct, and some of them formed in large numbers. There 

 are other dicotyledons, however, in which the flowers are still more 

 simple in structure. Some of the flowers which we have studied 

 show different steps in the consolidation of parts of the flower. 

 In the evening primrose the sepals are united among themselves 

 (gamosepalous), and are adnate with the ovary, while the petals 

 and stamens are seated on the calyx tube instead of on the recep- 

 tacle of the flower. In the " butter and eggs," not only is the 

 calyx formed by the united sepals, but the corolla is formed by 

 the united petals (gamosepalous). In the morning glory, calyx, 

 corolla, and pistils all show a union of their parts, i.e., the calyx 

 is gamosepalous, the corolla is gamopetalous, and the pistil is 

 compound. But they are all free, except the stamens, which are 

 inserted on the inside of the corolla. In the composites the 

 calyx tube, formed by the union of the sepals, is consolidated 

 with the outer wall of the ovary, while the calyx limb or free part 

 is reduced to mere scales or hairs, or is inconspicuous. The 

 corolla tube, or " ray," formed by the union of the petals, is 

 seated on the edge of the calyx tube. The stamens, united by 

 their anthers, are joined to the inside of the corolla tube. The 

 pistil is compound as shown by the divided style, but there is a 

 single cavity with one ovule which develops into a seed. The 

 walls of the ovule (seed coats) are consolidated with the ovary, 

 thus forming a one-seed fruit known as an akene. 



