THE EVOLUTION OF PLANTS 



597 



the megasporangium, which is enclosed in the integument. 

 In this connection it is of interest to note that the seeds of 

 some modern plants {e.g., orchids) do not possess differ- 

 entiated embryos, but whether this is a primitive or a 

 reduced character is not certain. The pollen was formed 

 in spindle-shaped pollen-sacs, having two chambers and 

 borne in clusters of four to six on the under side of little 

 oval discs from 2 to 3 millimeters long. These structures 



Fig. 419. — Top, lateral pinna from a leaf of Marattia Jraxinea. (After 

 Bitter.) Below at left, synangium of same. (After Bitter.) At right, 

 cross-section of the synangium. (After Hooker-Baker.) 



are found on pinnules of ordinary foliage leaves, resem.bUng 

 the sporophylls of certain ferns (Fig. 419) rather than the 

 stamens of modern flowers. 



The discovery of the seed-bearing character of the 

 fern-like plants of the Paleozoic was predicted by 

 Wieland, of Yale University, nearly two years before it 

 was made by Oliver and Scott. It is now believed that 

 seed-bearing plants of the pteridosperm type were nearly 

 as numerous in the Paleozoic as were the cryptogams. 



