Boodle.—■Anatomy of the Hymenophyllaceae. 475 
and Is found on the inner side of a protoxylem-group, but, 
in passing downwards, the fibres soon decrease in number 
until none are left. The protoxylem is then difficult to 
recognize In transverse sections, as there is only a small 
amount of parenchyma accompanying it, not a conspicuous 
group such as occurs in T. radicans. The protoxylem 
tracheides are mostly spiral. 
In transverse section the petiolar bundle has the outline 
of a truncated triangle with the base bulged in. The central 
region of the bundle is occupied by a large mass of fibres 1 , 
round which the xylem and phloem form two parallel bands, 
but are both interrupted at the middle of the upper side. 
The xylem thus forms a long band In the form of a flat-topped 
arch with its ends turned in. The protoxylem forms four 
groups at the four outer angles of the xylem. Besides the 
centrally placed sclerenchyma, several fibres occur singly or 
in small groups between xylem and phloem, and also embedded 
in the xylem. The fibres have small simple pits, and often 
have cell-contents. They are evidently derived from paren¬ 
chymatous elements, the central mass of fibres representing 
the central parenchyma of the petiolar bundle of T. radicans , 
or rather of some form with central parenchyma not containing 
protoxylem elements. The rest of the fibres found between 
xylem and phloem, and in the xylem, are derived from the 
conjunctive parenchyma-cells in these parts, and are just 
equal to them in size, but differ by their very thick walls. 
The occurrence of fibres inside a petiolar bundle is not very 
common among Ferns, but a similar large mass of fibres is 
found in Schizaea and in Adiantum trapeziforme , Linn. 2 
Prantl 3 describes the petiole of T. Prieurii as having three 
protoxylems, except just at the base where the dorsal group 
splits into two. The number of protoxylem-groups depends 
on the size of the xylem, which varies with the size of the 
1 Mentioned by Mettenius, Russow, Prantl, &c. 
2 Thomae, Die Blattstiele der Fame, Pringsheim’s Jahrb., XVII, 1886, p. 129. 
Potonie, Jahrb. d. k. bot. Gart. Berlin, II, 1883, p. 242. 
3 Prantl, 1 . c., p. 22. 
