414 THE VASCULAR PLANTS 



phytes of these plants being either insignificant little green 

 bodies, as in the common ferns, or parasites within the 

 sporophyte, as in seed plants. Evidently, then, the evolution 

 of a vascular system occurred after the principal nutritive 

 work of the plant began to be done by the sporophyte 

 generation. 



Vascular plants fall naturally into two great divisions, 

 those which produce seeds and those which do not. Those 

 which do not produce seeds are the pteridophytes. We 

 will consider them first. Among the pteridophytes are 

 found plants which are believed to be much Hke the ances- 

 tors of seed plants. 



Pteridophytes 



There are three divisions of pteridophytes. The com- 

 mon ferns with which you are famihar belong to one of 

 .these divisions. You recall that in bryophytes the mosses 

 are the most famihar and abundant members of that group. 

 They are the forms which give the group its name, and yet 

 they are not the forms of that group from which higher 

 plants were evolved. Similarly in pteridophytes, the ferns 

 are the most familiar members of the group and give ft its 

 name, yet it is not from ferns hke those of to-day that the 

 seed plants were evolved. 



The ancestors of seed plants were ferns of ancient 

 days-, long since extinct and not at all like modern ferns in 

 appearance. They were more Hke trees. Fossils of these 

 ancient ferns are abundant in those layers of rock from 

 which coal is principally obtained. (See Figure 206 A.) 

 Fossils are those evidences of once Uving things which we 

 find in rock. 



