Minnesota Plant Life. 415 



arose so that some flowers abandoned their stamens and pistils 

 and became converted into neutral ray flowers, useful in adding 

 to the attractiveness of the cluster, thus possibly inducing in- 

 sects to visit it more freely. The heads of flowers came them- 

 selves to stand in definite compound clusters, so that just as 

 there was a spike of fiowcrs in the plantain family there later 

 came to exist a spike of Hoivcr-hcads, as in blazing-stars, and 

 just as the flowers of the high bush cranberry learned to stand 

 in flat-topped clusters, so in the thoroughworts and asters, heads 

 of flowers were arranged in similar inflorescences. 



Each flower of the composite head shows a high degree of 

 fusion between its parts. That is to say, it is a flower of high 

 rank. The originally separate carpels are blended in pairs into 

 the fruit-rudiments, one to each flower. The stamens in all 

 Minnesota genera of composites except one are fused. The 

 petals of the corolla are blended into a tube which in some of 

 the flowers becomes split, to make the strap-shaped corolla of 

 the dandelion or the strap-shaped ray flower of the daisy. The 

 calyx parts are blended together into a calyx tube and this be- 

 comes fused with the surface of the fruit-rudiment, developing 

 in many of the genera a distributing apparatus made up of 

 bristles, variously arranged and of various structure. The 

 leaves below the flowering head, in such forms as the burdock 

 and cocklebur, become modified to assist the distribution of the 

 seeds. 



Three types of higher plants may be regarded as terminal. 

 the orchids standing at the top of the series of plants with one 

 seed leaf, the dogwoods at the top of the lower series of two 

 seed-leafed plants, and the sunflowers, dandelions and thistles 

 at the top of the highest series. Among orchids, the flower 

 cluster was not highly improved as such, but the perfecting 

 tendencies worked rather toward the production of a much 

 complicated floral mechanism, irregular in shape, reflecting the 

 strong influence of those forces which develop bilateral sym- 

 metry, and very exact in its adjustment to the habits of the 

 insects which co-operated in its pollination. The clusters of the 

 dogwood, although not so fully perfected as those of the sun- 

 flower, showed, in the arrangement of their flowers, some tend- 

 ency towards the perfection of the flower cluster as a unit. 



