386 DR. D. H. SCOTT ON BOTRYCHIOXYLON PARADOXUM, 
their true place in the direction of the Coenopteridez "* (Bower, '11!, p. 296), and 
emphasizes the anatomical comparison between the recent family and the Zygopterideze 
(Bower, "112, p. 546). Prof. Campbell, though he claims for the Ophioglossacez a more 
primitive position than most botanists would allow them, admits the possibility of a 
relation to the Botryopterideze (Campbell, '11, pp. 3 & 214). I have always recognized 
this affinity, and need only repeat what I said in 1909, that “of known plants it is the 
Botryopteridese which appear to have most in common with the Ophioglossaces ” 
(Scott, *09, p. 640). 
It is scarcely necessary for me to discuss the bearing of the facts here detailed on the 
theoretical question of the morphology of the pith. The matter has recently been fully 
dealt with by Prof. Bower (11? and ’11%), So far as the Zygopteridez are concerned, 
there seems no room for doubt that the parenchyma of the “ mixed pith” is of stelar 
origin; in fact, if we take the whole range of the Botryopterideze in the wide sense, 
we can trace the stages of evolution from an undifferentiated xylem-cylinder, first of a 
specialized internal xylem and then of the ** mixed pith " (Gordon, 11! and 112; Scott, 12). 
But in this fossil group we never get beyond a mixed pith; no known member of the 
Zygopteridez had got rid of its internal tracheides and arrived at a true pith. It is 
therefore only by bringing in other families, namely, the recent Ophioglossacez and 
both recent and fossil Osmundaceze (Kidston & Gwynne-Vaughan, 10; Gwynne- 
Vaughan, 711), that the argument for stelar medullation can be completed. The whole 
position assumes that the various Zygopteridean types of stem-anatomy are derived from 
a protostele; if we take the opposite theory, as held by Dr. P. Bertrand (112) that they 
arose by condensation of a polystelic structure like that of Cladoaylon, the question of 
the origin of the pith assumes a totally different aspect. Personally, I still incline to the 
former view. 
SUMMARY. 
1. The stele of Botrychiorylon paradoxum has a simple, nearly cylindrical form. There 
is a “mixed pith” consisting of internal xylem and parenchyma; the outer zone of wood 
is entirely secondary, diminishing in thickness towards the upper part of the stem. 
2. The cortex is of very uniform parenchymatous structure, and is bounded externally 
by periderm. 
3. The branching of the stem is dichotomous. 
4. The leaf-trace is given off from the stele ina similar manner to that of Ankyropteris 
corrugata. The xylem of the trace appears, like that of the stele, to be largely of 
secondary origin. 
5. The petiolar bundle only shows primary tissues. It has short antenne and a long 
median band (“apolar”). There appear to be no peripheral loops, the sinus at each end 
of the xylem being open. 
6. Aphlebiz are borne both on the stem and petiole ; they are branched, spine-like 
organs. 
* Prof. Seward's name for the Primofilices of Arber, including the Botryopterides of Renault. 
