RESULTS OF PAL.EONTOLOGICAL RESEARCH 73 



It does not therefore follow from the fact that in 

 the Carboniferous formation many ferns formed actual 

 trunks, that they are really related to the Gymnosperms 

 (Pteridosperms). On the other hand there may be 

 Gymnosperms (the said Pteridosperms) with fern-like 

 foliage. 1 



In the coal strata of the Tertiary formation the 

 flora of the present-day moors is much more similar, 

 ' since these formations contain many genera and species 

 of plants which still exist/ In North America we have 

 to-day ' very extensive moors with a plant community 

 of which a considerable number of species are the same 

 as, in the Miocene period, occupied our moors/ 3 



(3) Phenomena of Retrogression (p. 44). 



If our present Equisetse be compared with the 

 Calamariacese of the Carboniferous period, which are 

 closely allied, a general degeneration of those gigantic 

 tree-like growths might be assumed. In nearly all 

 educational books indeed we find the same observation 

 that our Equisetums, as small insignificant weeds, 

 of such great uniformity of make that all the species 

 only form one genus, 3 are the degenerated dwarfed 

 descendants of those fossil trees. If that be so, we 



1 In this case it is, in addition, quite immaterial whether the fern type 

 of the leaf be regarded as evidence of convergence or not, since even to-day 

 Gymnosperms exist with such foliage the Cycads (Fern Palms) which, 

 however, are not therefore regarded as ' intermediate forms.' Oliver 

 (Biol Zentralbfatt, 1905, p. 403) constantly speaks of * intermediate forms * 

 (Zwischenformen). 



2 Potonie : Die Entstehung der Steinkohle, etc., p. 185. 



3 Warming : Systematische Botanik, p. 151. 



