122 THE STORY OF THE EARTH AND MAN. 



belong inost of tlie ordinary trees of temperate 

 climates. To the second belong tlie palms and 

 allied trees found in tropical climates. To tlie third 

 belong the pines and cycads. In the second or 

 Cryptogamous series we have also three classes, — 

 (1.) The AcrogenSy or ferns and club-mosses, with 

 stems having true vessels marked on the sides with 

 cross-bars — the Scalariform vessels. (2.) The Ano- 

 phytesy or mosses and their allies, with stems and 

 leaves, but no vessels. (3.) The ThaUophytes, or 

 lichens, fungi, sea-weeds, etc., without true stems 

 and leaves. 



" In the existing^ climates of the earth we find 

 these classes of plants variously distributed as to 

 relative numbers. In some, pines predominate. In 

 others, palms and treo-ferns form a considerable 

 part of the forest vegetation. In others, the ordinary 

 exogenous trees predominate, almost to the ex- 

 clusion of others. In some Arctic and Alpine 

 regions, mosses and lichens prevail. In the Coa] 

 period we have found none of the higher Exogens, 

 though one species is known in the Devonian, and 

 only a few obscure indications of the presence of 

 Endogens ; but Gymnosperms abound, and are 

 highly characteristic. On the other hand, we have 

 no mosses or lichens, and very few algae, but a 

 great number of ferns and Lycopodiaceas or club- 

 mosses. Thus the coal formation period is botanically 

 a meeting-place of the lower Phaenogams and the 

 higher Cryptogams, and presents many forms which. 



