THE HOMOSPOROUS LEPTOSPORANGIATJE 



361 



sists of small ringed and spiral elements constituting the proto- 

 xylem, and larger scalariform metaxylem tracheids. In O. 

 cinnamomea, Faull found an internal endodermis and traces of 

 internal phloem, which are quite absent in the other species, 

 where the xylem-masses are in direct contact with the pith. 

 Faull considers the condition in 0. cinnamomea as the primitive 

 condition from which the type found in the other species has 

 been derived by a suppression of the inner phloem and endo- 

 dermis. 



A. 



B. 



FIG. 204. Osmunda regalis. A, Part of the central cylinder of the rhizome, X25o; 

 B, a sieve-tube, more highly magnified. (After Zenetti.) 



The leaf traces (Faull (i), p. 20) pass very obliquely 

 through the cortex into the leaf base. They are concentric in 

 structure. The protoxylem is situated on the inner face of the 

 xylem strand and is continuous with that of the stem. Each 

 leaf trace is surrounded by a sheath of colourless cells. 



The Leaf 



The origin of the leaves is the same as in the Polypodiacese, 

 but the young leaf grows from a three-sided apical cell much 



