xxix] 



DICKSONIEAE 



265 



in diameter in a large stem ; but still there is no medullar) vascular system 

 this is one of the largest examples of a purel)- parenchymatous pith. 



Fio-. 533. Dkksonia antardka R. Br. Transverse section ofstem, showing highly corrugated 

 * stele, and large pith without any medullary vascular system. (| natural size.) 



SoRus AND Sporangia 

 The proof that the receptacle of the Dicksonieae is really marginal 

 origin is of considerable importance in their comparison 

 with other Ferns. It is shown to be so by the segmenta- 

 tion of the very young fertile pinnule (Fig. 534). It is 

 then seen that the marginal cell {K) projects between 

 the upper and lower indusia [U, L), which originate b}- 

 upgrowths of its segments. The correspondence with 

 Hymenophyllum (Fig. 513), and Thyrsopteris (Fig. 529) 

 is very close. A later stage is shown in Fig. 535,^, where 



already the marginal receptacle {in) is covered in by ^^^^^^ ^,,^^^^ 

 the massive indusial lips. A section parallel to the of C%otium Scheidd. 

 leaf-surface {z, z) shows that the receptacle is flattened ^^ff ^J^p^^T'^tSum. 

 and elongated {B), while a transverse section at the A = Lower indusium. 



