74 



THE THEORY OF EVOLUTION 



have certainly here a good example of a general retro- 

 gression before us. That would not be an impossibility, 

 since, supported by the comparative study of the present 

 moorland flora and the fossil one, the thickening of the 

 stems, the abundant ramification of the lateral growths, 



the form of the 

 leaves, which are 

 not increased in 

 area but only split 

 up (Fig. 24), may 

 all be imputed to 

 the influence of the 

 favourable environ- 

 ment in the Carbon- 

 iferous period. If 

 such conditions 

 cease, naturally all 

 the special con- 

 forming structural 

 arrangements cease 

 also. Therefore the 

 lack of thickened 



stems, the reduction of leaf area, and the reduced 

 branching of the present forms, can scarcely be called 

 an actual degeneration. But in the Carboniferous 

 period there were in all probability weed-like small forms 

 as well as the gigantic ones ; l and from these we might 

 well attempt to deduce the modern Equisetae. Certain 

 it is that the existence of small club-mosses is proved. 



1 Gothan : Entivicklung der Pflanzenwelt, p. 51. 



Fie. 24. CALAMAKIA FOLIACE. (After 



a, Asterophyllites equisdiformi-s : Carboni- 

 ferous, Harz. b, Annular ia splienophyl- 

 Idides ; ZAvichau. c, A. radial a ; Lo\\er 

 Silesia. The leaves have not assumed scale- 

 like forms as have the present ones. 



