a ae 
420 Structural and Physiological Botan eee ” « 
In reference to the relative position of the an and to 
the fossil remains (chiefly those of animals) found in them, a | 
number of geologzcal systems are distinguished, which are again 
divided into groups. . 
The lowest strata of the Primary or Paleozoic age (de e. 
the period of the oldest living beings)—vzzz. the strata of the 
Szlurian' system—contain the earliest remains that have 
been preserved of the vegetable world. Only a few marine 
Algee are known ; but others may have altogether perished, 
their existence Heme indicated only by the occurrence of 
carbonaceous or bituminous limestone. 
In the Devonian system the number of species, genera, 
and families has greatly increased. In addition to a con- 
siderable number of Algee, the first land-plants have made 
their appearance. ‘They consist almost entirely of the re- 
mains of Vascular Cryptogams, with a few Cycadeze and 
Conifere. The aspect of this period, as also of that next . 
in succession, must have been extraordinarily uniform and 
monotonous ; but vegetable life had extended over the sur- 
face of the earth in a variety and luxunance of forms far 
surpassing our existing vegetation. 
In the Carboniferous period Ferns attained a special de- 
velopment. We find lofty trees or shrubs with multipinnate‘ 
leaves several feet in length, forming magnificent groups of © 
plants, in the shade of which other smaller species grew 
_as underwood (Figs. 540-542). Among the largest forms — 
of which these forests were composed were certain Lyco- — 
podiaceee—to which nothing now existing is comparable ~ 
—known as SzgeHarie aud Lepidodendra (Figs. 535-539). 
gens, 43 genera, 142 species; Gymnosperms, 56 genera, 363 species; 
Cryptogams, 152 genera, 1,172 species; Doubtful, 35 genera, 197 a 
species. Since that time the number of both genera and species has been 
enormously increased, especially by the additions to the Tertiary flora — 
made by Heer and Ettingshausen. —-ED.] 
1 [Geologists now distinguish the oldest stratified beds from the 
superimposed Silurian as the Laurentian and Cambrian systems. They 
-contain but few remains of organic life. —ED. ] 
: = nw 
