Origin of Medullation in the Ophioglossaceae. 5 51 
4. Subsequently in Botrychium there is a further intrusion of foliar 
pockets, delimited from the primary pith by endodermis. The definitive 
pith column is thus derived from three distinct sources : (a) intraxylic 
parenchyma, (b) conjunctive parenchyma, and (c) intrusive parenchyma of 
the leaf-pockets. 
5. The endodermal limits in Botrychium are usually maintained in 
the lower part of the stock, and the inner endodermis may be held to 
indicate (as the internal endodermis of Van Tieghem and Poirault) the 
distinction between the intrastelar and the intrusive pith. But the endo¬ 
dermis is gradually obliterated in the upper region. In Ophioglossum the 
endodermis is less distinct from the first. The obliteration is probably 
connected with the fact that the whole parenchymatous system of the 
stock serves the function of storage, and physiological barriers are not 
required. 
6. The primary xylem in Botrychium is in part or almost wholly 
replaced physiologically by the secondary xylem, which originates from 
the cambium. In the mature stock it is vestigial, and may be represented by 
the innermost tracheides of the xylem, together with occasional isolated 
tracheides, or groups of them, which are found about the periphery of the 
parenchymatous pith. 
7. But in Botrychium ternatum a traumatic condition in a certain 
specimen showed tracheides scattered throughout the pith, even to its 
centre. If this be held to be a reversionary state, the facts would indicate 
that in this species the pith to its centre was originally stelar. A some¬ 
what similar state has been observed in a sporeling of Botrychium Lunaria. 
8. A comparison of this traumatic state of B. ternatum with the fossil 
named by Scott Botrychioxylon shows substantially the same structure. 
A close similarity exists on the other hand with young plants of Helmin- 
thostachys , supposing the secondary thickening of Botrychium to be absent. 
9. The conclusion from these observations is that the pith in the 
Ophioglossaceae is primarily, though not always wholly, of intrastelar 
origin, and that the pith is in part at least intraxylic in origin. 
10. A comparison of the sporeling of Osmunda cinnamomea y as 
described by Faull, shows that, up to the twelfth leaf at least, the origin of 
the pith is intrastelar also, and corresponds to that of Botrychium before 
any intrusion of foliar pockets has occurred. 
11. As the ontogenetic history for the two families runs parallel with 
the history of the fossil Osmundaceae, as disclosed by Kidston and 
Gwynne-Vaughan, it is concluded that an intrastelar pith was formed first 
in the descent both of the Osmundaceae and of the Ophioglossaceae, and 
that an intrusion of foliar pockets may have followed, varying in extent 
according to the proportion of leaf to axis in the individuals of the two 
families. 
