536 BOTANY PAHT n 



Marattiaceous ferns. Their fronds (tiphenopteris, Fig. 505 ; Neuropteris) were 

 highly compound, the main rachis dividing dichotomously above the base. The 

 stem had axillary branching (Lyginodendrori) and underwent secondary thickening 

 by means of a cambium ; this cut off radially-seriated xylem elements to the 

 inside and phloem to the outside (Fig. 506). The leaf-trace bundles met with 

 in the cortex traverse the zone of wood to unite with the strands of primary 

 xylem at the periphery of the pith. The roots also underwent secondary 

 thickening. 



The Pteridosperms were heterosporous ; the sporangia were borne on fronds 

 that resembled those of ordinary ferns. The microsporangia (Crossotheca, Fig. 

 507 A) showed resemblances to Matattiaceae ; the macrosporangia (Lagenostoma, 

 Fig. 507 B), on the other hand, were surrounded by a cupule and resembled in 

 construction the ovules of the Cycadeae ; the macrosporophylls were not, however, 

 arranged in cones. 



