6l8 STRUCTURE AND LIFE HISTORIES 
modern vascular plants, substantially as indicated in 
Fig- 434- * 
(6) 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 
1 Scott restricts the name Lycopsida to the Lycopodiales, and proposes 
a third group, Sphenopsida, including the Equisetales, Pseudoborniales, 
Sphenophyllales, and Psilotales. 
