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. 
