564 Bower. — On Medullation in the Pteridophyta . 
the family, together with reference to one relatively recent fossil. It is 
held by Professor Jeffrey and his pupils. But they have not advanced 
any evidence in support of it from early fossils. It would strengthen their 
case if they were to produce specimens of the reputed ancestors, showing 
the 4 amphiphloic siphonostelic ’ structure, from early strata. But this has 
not yet been done. The other view is that the present condition shows the 
approximate limit of an up-grade development, which arose from a protostelic 
state, without the amphiphloic siphonostele having figured in the earlier 
stages at all. It has been based upon the study of a stratigraphical 
sequence of related fossil forms carried out by Kidston and Gwynne- 
Vaughan. This view would ascribe the origin of the pith to direct 
medullation of the protostele. The alternative view would be that the 
pith originated wholly by intrusion of the cortex through the foliar gaps, 
according to Professor Jeffrey’s generalization. If the present Osmun- 
daceous structure has really been reduced, the fossil correlatives should 
indicate progressively a nearer approach to a condition of amphiphloic 
siphonostely. But, with the exception of the relatively late Osmundites 
skidigatensis , the reverse has been shown to be their general trend. The 
facts and arguments of Kidston and GWynne-Vaughan are now so well 
known that they need not be recapitulated here: nor yet the rejoinders 
with which they have been met by the other side. 1 It will suffice to 
consider the facts as stated by Kidston and Gwynne-Vaughan for the 
Osmundaceae from the point of view of the hypothesis above propounded. 
What we should anticipate, if it were true, would be that the stele should 
show intrastelar pith in accordance with the constant and phyletically erect 
position of the axis. Also that there should be some degree of formation 
of foliar gaps in accordance with the megaphyllous character. Kidston and 
Gwynne-Vaughan have shown, and illustrated by photographs of sections, 
and by diagrams, the existence of imperfect foliar pockets in Osmundites 
Kolbei and skidigatensis , two of the more recent fossil types. They are 
comparable in essentials with those relatively small pockets found in the 
1 The Fossil Osmundaceae : Parts I-IV, Trans. Roy. Soc. Edin., 1907-10; Jeffrey, Bot. Gaz., 
Jan., 1908, p. 67, and Nov., 1908, p. 395 ; also Bot. Gaz., 1910, pp. 401, 476 ; Faull, Trans. Can. 
Inst., vol. viii, p. 515, &c.; Sinnott, Ann. of Bot., 1910, p. 107. It is interesting to note how, in 
the last-named work, doubts of the accuracy of the observations of Kidston and Gwynne-Vaughan 
grow in the course of a few pages to full assurance of their error in the interpretation of a fossil 
which the critic has never seen. On p. no Sinnott, writing of 0 . Dunlopi, remarks: 1 it seems 
entirely possible that very narrow rays . . . might have occurred.’ This suggestion is based on ‘the 
present indifferent state of preservation’ of a fossil he has never personally examined. On p. m 
his statement on the same fossil is strengthened thus : ‘ On the whole it seems very probable that we 
have here to deal with a form . . . where foliar gaps were always present’ At the conclusion of the 
paper the general statement which covers 0. Dunlopi , together with the rest, is couched in still 
stronger terms (p. 116) thus: ‘ From such fossil evidence as is available therefore ... it seems quite 
clear that the presence of foliar gaps is a primitive feature in the Osmundaceae.’ The italics are 
mine. Readers will form their own estimate of the value of evidence thus accumulated in support of 
a favoured theory. 
