6l8 STRUCTURE AND LIFE HISTORIES 



modern vascular plants, substantially as indicated in 



Fig- 434-^ 



(b) Greater precaution in drawing conclusions from the 

 few known facts has led still other students of fossil plants 

 to refrain from endeavoring to connect up the ancestral 

 lines, claiming that while they may converge, indicating a 

 common ancestry of the known forms in the geologic past, 

 on the other hand they may not unite, or at least may not 

 all converge toward the same ancestral type. In other 

 words, it is suggested that fossil and modern plants had a 

 polygenetic origin from the stage of primitive protoplasm. 

 Such views are illustrated in Table VII (p. 619). 



It is seen from this diagram that our modern ferns have 

 a long ancestral history, extending from the present back 

 to early Palaeozoic times ; the same is true of our modern 

 cycads, maidenhair tree (Ginkgo), club-mosses (Lyco- 

 podiales), and horse-tails (Equisetales) . The Coniferales 

 may be traced back into the upper Carboniferous period, 

 while the most highly developed of modern plants, the 

 Angiosperms, appear to have come into existence as late 

 as about the middle of the Mesozoic era, perchance as 

 recently as 20 million years ago. 



"The construction of a pedigree of the Vegetable King- 

 dom is a pious desire, which will certainly not be realized 

 in our time; all we can hope to do is to make some very 

 small contributions to the work. Yet we may at least 

 gather up some fragments from past chapters in the history 

 of plants, and extend our view beyond the narrow limits 

 of the present epoch, for the flora now living is after all 



' Scott restricts the name Lycopsida to the Lycopodiales, and proposes 

 a third group, Sphenopsida, including the Equisetales, Pseudoborniales, 

 Sphenophyllales, and Psilotales. 



