546 Bower.—On the Primary Xylem , and the 
Jeffrey, has its important bearing as indicative of the intrastelar origin 
of a substantive part of the pith in the Ophioglossaceae. 
Comparing the three genera of Ophioglossaceae, it is seen that the 
structure of all of them is referable in origin to the protostele, in which 
the xylem may be composed at first entirely of tracheides, as seen in the 
various species of Ophioglossum , and it appears to be the case also in some 
specimens of Helminthostachys - 1 Or a few parenchyma cells may be 
intermixed with the tracheides, as is more common in Helminthostachys , 
and in Botrychium. But, alternatively, in all the three genera the stele 
may be medullated from the first. In this respect there is inconstancy even 
in the single species. Whether initially medullated or not, a pith of some 
sort is formed in all cases before the departure of the first leaf-trace. Onto- 
genetically it is of intrastelar origin, and its source is by accumulation of 
the parenchyma of the xylem at the centre of the stele, added to, when the 
xylem-ring opens, by some degree of intrusion of the conjunctive tissue; 
but this is certainly not the only source. Its original source appears to be 
the former, and the occurrence of isolated tracheides, or groups of them, 
about the margin of the pith (PL XLV, Figs. 14-16), as well as the changes 
following on injury seen in B. ternatum , support this conclusion. 
In Ophioglossum and Helminthostachys there is no cambium. But in 
Botrychium a secondary activity appears early, and most of the wood is so 
produced. The primary wood is accordingly vestigial in most species, 
though it may be fairly represented in B. Lunaria. The resulting condition 
may be compared with that seen in the fossil Botrychioxylon , recognized and 
briefly described by Scott. 2 The full description of this stem with figures 
will be awaited with increasing interest. Dr. Scott kindly showed me the 
specimens for the purpose of this comparison. The stele has centrally 
a core composed of tracheides scattered through a parenchymatous matrix. 
This represents the primary wood, and compares with that of the young 
stem of Helminthostachys (PL XLVI, Fig. 22), or of Botrychium (PL XLV, 
Figs. 10,11). A broad band of secondary wood surrounds it, which corresponds 
to the secondary wood of Botrychium. The similarity between the fossil and 
the traumatic condition of B. ternatum (PL XLVI, Figs. 18-20) is specially 
striking, while, on the other hand, the comparison may be drawn with certain 
of the Botryopterideae, and especially with the stem of Zygopteris , which 
shows a central differentiation of the xylem along somewhat similar lines. 
The course of development of the stock in the Ophioglossaceae shows 
a further factor, absent in the first steps of medullation, but increasingly 
important as the plant becomes established and the individual leaves attain 
larger size. It is the intrusion of foliar pockets. As PL XLV, Fig. 8, shows, 
1 Lang, Ann. of Bot., vol. xvi, p. 42 : ‘ The xylem is in some cases a solid central strand.’ 
2 Journ. Roy. Micr. Soc., 1906, p. 519; and somewhat more fully in Progressus Rei Botanicae, 
Bd. i, 1906, p. 181. 
