420 THE CARBONIFEROUS PERIOD 



the present time, the Lycopods have dwindled to a few insignifi- 

 cant herbaceous forms, but in Carboniferous times they were the 

 abundant and conspicuous forest trees, at least of the swampy 

 lowlands. One of the most characteristic of these trees was 

 Lepidodendron (PI. VI, Fig. 12), of which many species have been 

 found in the coal measures. These great club-mosses had trunks 

 of 2 or 3 feet in diameter and 50 to 75 feet high, which pos- 

 sessed the remarkable quality, for a Cryptogam, of an annual 

 growth in thickness. At a considerable height above the ground 

 the trunk divides into two main branches, each of these again into 

 two, and so on (dichotomous division). The younger parts of 

 the tree are covered with long, narrow, stiff, and pointed leaves, 

 while the older parts are without leaves, which have dropped off, 

 making conspicuous scars, arranged in spiral lines around the 

 stem. At the ends of the twigs in some species, or on the sides 

 of the trunk and larger branches, in others, are found the spore- 

 bearing bodies, which have much the appearance of pine-cones. 

 The stem was, to a large extent, filled with loose tissue and had 

 only a relatively small amount of wood. 



Another very characteristic and abundant tree is Sigillaria ; it 

 is closely allied to Lepidodendron, but has a very different appear- 

 ance. The trunk is quite short and thick, rarely branching, and 

 with a pointed or rounded tip, much as in the great Cactus ; the 

 leaves are similar to those of Lepidodendron, but are arranged in 

 vertical rows. Sigillaria also possessed the power of annual in- 

 crease in diameter. Both Lepidodendron and Sigillaria are pro- 

 vided with branching rhizomes, or underground stems, which carry 

 finger-like appendages inserted into pits. Before the nature of 

 these rhizomes was understood, they were regarded as distinct 

 plants and named Stigmaria. 



A third group of Cryptogams, the Equisetacece, or Horsetails, 

 were of great importance in the Carboniferous forests. The 

 Catamites were decidedly superior to the existing horsetails, not 

 only in size, but in many features of organization as well. These 

 plants had tall, slender stems divided by transverse joints, with 

 a soft inner pith, surrounded by a ring of woody tissue, which 



