XVIII] 



ZYGOPTERIDEAE 



The details of this remarkable fossil are seen in Fig. 323. The stellate 

 stele consists of xylem which is all primary, showing as in Aukyropteris a 

 distinction of external tracheides of wide, and internal tracheides of narrower 

 lumen. Outside this there is phloem with large sieve-tubes, surrounded 



Fig. 523. Asterochlaena laxa : specimen showing in transverse section the whole stellate stele, with 

 the neighbouring leaf-traces. Prep. 484^, 2 a from the Solms-Laubach collection. The foliar traces 

 are verticillate, with alternating sequence, ten in each whorl. (After P. Bertrand.) 



