496 



HISTORICAL GEOLOGY 



(5) Horsetails (Calamites) . — Except for their greater size, the 

 horsetails of the Carboniferous had much the appearance of the lowly- 

 horsetail or scouring rush of to-day and were, indeed, related to it. 

 The tree horsetails of the Paleozoic are called Calamites (Fig. 475), 

 from the most important genus of that time. They were trees which 

 reached a height of 60 or more feet and were almost as conspicuous as 



their Lepidodendron and Sigillaria 

 neighbors. Their habit of growth ap- 

 pears to have been similar on a glorified 

 scale to that of some of their living 

 relatives. Some were simple shafts, 

 while others were probably gracefully 

 branched trees with many boughs. 



The bark (Fig. 476 A) of the Cala- 

 mites had characters which readily 

 distinguished it from other trees of its 

 time. The stems were ribbed, the ribs 

 ending at each "node" and a new set 

 continuing beyond the node to the 

 next, when an alternate set again ap- 

 peared. The leaves (Fig. 476 B) were 

 simple and were attached to the nodes 

 in whorls. Conelike fruits were borne 

 at the ends of the twigs and contained 

 spores of one kind. 



Calamites began in the Devonian 



and went out with the Paleozoic, but 



the horsetails of the Mesozoic were 



Fig. 475. — Calamites. They transitional, both in size and in struc- 



seem to have had habits similar to ture, to the modern horsetails. 



those of the horsetails of to-day. (6) Cordaites and Qther Gymno . 



(See Fig. 476 A and B.) w J 



sperms. — 1 he trees or this group were 



the most highly developed of the Paleozoic forests. They were large 

 trees (Fig. 477) which sometimes grew to be 100 feet in height and 

 were easily distinguished from the other trees of the time by the 

 large, sword-shaped leaves which were borne in a crown on the top of 

 the main trunk. Some specimens of Cordaites leaves exceed three feet 

 in length and closely resemble the leaves of such plants as the lily and 

 Indian corn, although not related to them. The fructifications, which 

 were borne in a poorly developed cone, were of two kinds, male and 



