296 INTRODUCTION TO BOTANY 
that seed plants were also present during that time. It was 
later, during the next age, that gymnosperms 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 
