138 



OSMUNDACEAE 



[CH. 



there is at first a prostele without internal complications, which expands 

 later and becomes medullated. The first seven or eight leaves have a proto- 

 stelic departure: after the medullation of the xylem the ring is breached by 

 a xylic gap at the departure of each trace, but there are never true foliar 

 gaps with continuity of pith and cortex. The changes are all intra-stelar, 

 and remain so to the adult state. Thus the ontogeny suggests a progressive 



Jig 429 PaiL 1 u in-,\i.i^i. Lc 1 111 of 1 I'li 

 (Kicliwakl), «, oiiltr \ylcm ; b, irner \\km 

 Frutii Seward.) 



Ill in 1 ^ I i_iii II u / iiiinof-hns \i/il hhiiJahi 



(Aflei Kidsion and Cj\\yiine \ au^lian, \li\ ^li^htly reduLcd. 



evolution from the protostele which stops short at the state attained by the 

 adult (Faull, Trans. Can. Inst, viii, p. 515, 1909; Gwynne-Vaughan, Ann. 

 of Bot., xxv, p. 525, 191 1). 



More cogent evidence than this is derived from the study of the structure seen in related 

 fossils. This work has been carried out by Kidston and Gwynne-Vaughan, and the 

 demonstration is a very convincing one. {Trans. Roy. Soc. Edin. No. I, xlv, p. 759, 1907. 

 No. II, xlvi, p. 213, 1908. No. Ill, xlvi, p. 651, 1909. No. iv, xlvii, p. 455, 1910. No. v, 

 1, p. 469, 1914.) If the stelar structure of the living Osmundaceae be of a reduced type, the 

 fossil correlatives should show a progressively more complex structure of the stele as they 



