PALEOBOTANY BERRY. 337 



seeds (Sphaerostoma) are small with an inner integument and an 

 outer integument or cupule, both with an elaborate vascular supply. 

 The free apical part of the nucellus is a relatively flat plinth sur- 

 mounted by a central dome or lagenostome, which is surrounded by an 

 annular pollen chamber. The free apical part of the integument 

 formed a frill or canopy with eight radial crests around the micro- 

 pyle. Heterangium has a greater range than Lyginopteris, being 

 found from the Lower Carboniferous to the Permian. Seeds of Lygin- 

 opteris or Heterangium are found in the French Coal Measures asso- 

 ciated with the frond genera Sphenopteris elegans, S. dissecta, and 

 /S. obtuslhba. 



A second family type to which at least four genera are referable is 

 the Medullosaceae. These are characterized by the enormous devel- 

 opment of the fronds of the Neuropteris and Alethopteris type with 

 petioles several centimeters in diameter. This enormous display of 

 foliage is doubtless to be correlated with the peculiarities in the 

 anatomy of the stems. The most primitive known genus, one indi- 

 cating the point of departure of the other and more specialized mem- 

 bers of the family is Sutcliffia of the English Lower Coal Measures. 



Sutcliffia had a large pithless central stele of centripetally formed 

 wood from which meristeles branch and divide and fuse irregularly 

 and eventually give rise to leaf traces, a large number of which enter 

 each petiole, where their structure is concentric. Secondary wood is 

 but feebly developed. The next stage in the evolution of these forms 

 away from the Heterangium type is furnished by Medullosa anglica, 

 which is polystelic with normally three steles each developing second- 

 ary wood. The steins were as much as 7 or 8 centimeters in diameter 

 and bore spirally arranged decompound fronds with decurrent 

 petioles. Many adventitious roots were formed. 



Without stopping to dwell on the histological details we pass to the 

 exceedingly complex Medullosas of the Permian, in which the steles 

 become very numerous and are differentiated into inner " star rings" 

 and outer " plate rings " systems, the latter forming a peripheral zone 

 which is an almost closed woody cylinder. Successive extrafascicu- 

 lar zones of wood and bast were developed in several species. The 

 leaf traces which are at first concentric break up into strands with 

 external protoxylem, several from different levels of origin entering 

 each petiole. The peculiar arrangement in these later Medullosas is 

 a necessary outcome of large polystelic stems with secondary thick- 

 ening and appears to have constituted a rather impractical experi- 

 ment in attempting to develop secondary thickening around numerous 

 steles in a single stem. If the theory advocated by Worsdell, Chodat, 

 and others is substantiated, it would appear that certain of the Per- 

 mian Medullosas solved this problem in the mechanics of stem struc- 

 ture by suppressing the centripetal portions of the steles, while the 



