29-i EVOLUTION OF PLANTS 



The Angiosperms are preeminently the modern plant 

 type. These have largely crowded out the other earlier 

 types of vegetation, and at present comprise a large 

 majority of existing species. In the earlier geological 

 formations, Pteridophytes and Gymnosperms predomi- 

 nated; but as the later formations are examined, the 

 Angiosperms become more and more important, prob- 

 ably first appearing in the Mesozoic age and rapidly 

 increasing in number and variety in the more recent 

 formations. 



It is among the Angiosperms that the plant body 

 reaches its highest expression. In the keen struggle 

 for existence among the manifold forms of plants, the 

 Angiosperms have shown themselves to be extraordina- 

 rily plastic, and have developed every possible device 

 to enable them to survive this fierce competition. This 

 is especially shown in the extraordinary variety of the 

 floral structures to which they have given rise. The 

 primitive flowers were doubtless very inconspicuous 

 and, as in the case of many existing flowers of similar 

 character, were dependent upon the wind or upon cur- 

 rents of water for conveying the pollen to the stigma. 

 This uncertain mode of pollination involves a great 

 waste of pollen, and evidently any device which insures 

 a saving of pollen is advantageous. This has been ac- 

 complished by the adoption of insect aid in pollination. 

 This probably began by the casual visits of insects to 

 flowers for their pollen, some of which was transferred 

 to the pistil of the next flower visited. Any flower 

 which, by reason of its brighter color or stronger odor, 

 made itself more noticeable to insects searching for pol- 

 len, would naturally stand a better chance of being vis- 



