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 M arattia 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, resembling 

 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. 



