COENOPTERIDACEAE 



[cii. 



Series to the Permian, where the large upright stems of AsterocJilaena laxa 

 appear in the Lower Permian of Saxony, and two species of Ankyropteris 

 have been found in the Permian of Autun and of Bohemia. After this 

 Period they appear to have died out. 



Vegetative Structure 



The conformation of the shoot in the Zygopterideae, and its internal 

 structure as well, are probably the best known in Ankyropteris, which 

 appears to have consisted of small plants with thin stems, and an upright, 

 perhaps straggling or even climbing habit. The stems branched, sometimes 

 by equal distal dichotomy as in Ankyropteris corrugata (Fig. 318), sometimes 

 unequally so that the weaker axis lying between the stronger and the base 



l.t. 



Fig. 318. Ankyropteris corrugata. Transverse section of a dicho- 

 tomous stem, showing the two steles. The stele on the left has a 

 band of secondary wood at x' ; l.t., leaf-trace. ( x about 8.) From 

 a photograph by Mr W. Tains. S. Coll. 2715. (After Scott.) 



of a subtending leaf appears as an axillary shoot. This is seen in A. Grayi 

 (Fig. 319), and it occurs also in other species (Scott, p. 295). In view of the 

 fact that the axillary shoot repeats on a simpler scale the anatomy of the 

 relative main axis, the conclusion may be accepted that this is its real 

 nature. The condition thus seen appears to have resulted from development 

 of a dichotomy derived primarily from equal dichotomy such as is seen in 

 A. corrugata, but with one of the shanks arrested. It is to be noted that 

 equal dichotomy is also a character of Botrychioxylon, Dineiiron, and some 

 others. 



The leaves of the Zygopterids were relatively large, and probably upright 

 in their habit. They consisted of a stout rachis traversed by a meristele 



