296 INTRODUCTION TO BOTANY 



that seed plants were also present during that time. It was 

 later, during the next age, that gymriosperms became most 

 abundant. There are fossil remains of giant gymnosperms 

 trees so well preserved that even the nature of the seeds may 

 be determined. In those times gymnosperms were everywhere. 

 The " big trees " and redwoods extended to Greenland, and 

 other groups now well-nigh extinct grew in profusion over 

 very wide areas. Pines did not become abundant until late 

 in the development of gymnosperms, and they are still widely 

 distributed and fairly luxuriant in their growth. No doubt 

 the climate and physical conditions upon the earth have 

 undergone very extensive changes during the earth's history, 

 and in consequence plant life has changed. Therefore the 

 plants now surviving from former abundant groups have prob- 

 ably undergone many alterations since the times when their 

 ancestors were dominant. But they stand as living evidences 

 of the kinds of plants that were most abundant before the last 

 great group became the dominant plants of the earth. That 

 group is the angiosperms. 



281. Angiosperms : their diversity. This is the second 

 group of the seed plants and is therefore the highest group 

 of the plant kingdom. Angiosperms exhibit the widest varia- 

 tion in form and in habits of living. As water plants they 

 may be submerged or free-floating, or may grow in water part 

 of the time and on land part of the time ; they may grow in 

 regions that are so dry and exposed as to make life seem 

 impossible. They thrive luxuriantly in the tropics, and even 

 live upon the ice in frigid regions. They may live as epiphytes, 

 or as vines climbing upon other plants. They may be parasites, 

 saprophytes, or even carnivorous plants. In form the angio- 

 sperms range from diminutive floating disks to gigantic trees. 

 In length of life they range from those that complete their life 

 round many times during one year to individual plants that 

 live to be several centuries old. 



The total number of species of angiosperms is not definitely 

 known, but botanists agree that there are over one hundred 



