EVOLUTION OF SEED-PLANTS 117 



dophyta were in Mesozoic times the leading class 

 of plants, abounding, as their remains prove, in 

 every part of the world, and attaining to the high- 

 est development which any plants had reached 

 at that period. 



When we go back to Palaeozoic times, we find 

 the Cycad line represented by a vast mass of 

 forms, probably no less extensive than the Cyca- 

 dophyta of the Mesozoic, very highly developed 

 on their own lines, but more primitive, in so far 

 as they were more Fern-like, than the Cycado- 

 phytes themselves. This race, on present evi- 

 dence, is as ancient as any class of land-p'lants 

 with which we are acquainted. 



If, as we have found reason to believe, the 

 Cycadophyta, in one or other of their branches, 

 gave rise to the true Flowering Plants, it appears 

 that the same great race has played a leading part 

 throughout geological history, from the De- 

 vonian onwards, first as the Pteridosperms, then 

 as the Cycadophyta, and finally as the Angio- 

 sperms which still prevail. 



Probably some Pteridosperms lingered on into 

 the Mesozoic period, but they were mostly re- 

 placed by Cycadophyta; in like manner some few 

 Cycads have persisted, through the Tertiary, 

 down to our own day, but as a dominant class 

 they are replaced by the higher Flowering Plants. 

 Each prevalent class in turn has given rise 



