Boodle. » — ■ Anatomy of the Schizaeaceae. 369 
very thick-walled sieve-tubes are present, and resemble fibres, 
but were not lignified in the cases examined. 
The petiole of Z. palmatum is small compared with that of 
Z. dichotomum , &c., and is of a somewhat different type. The 
xylem is shaped rather like an equilateral triangle with one 
protoxylem at each corner. The protoxylem-group on the 
lower side is distinctly not peripheral, but slightly embedded 
in the xylem. This fact and the peculiar rosette-like arrange- 
ment of the adjacent tracheides round the protoxylem-groups 
in this species were noticed by Prantl (" 81 , p. 27). Especially 
in this species the rule given by Bertrand (’ 81 , p. 15), that in 
sections of appendicular organs the bundles show symmetrical 
arrangement in relation to a single straight line, does not at 
first sight appear to hold good, as the bundle has a nearly 
complete radial symmetry. But it must be noted that the 
median protoxylem (‘ centre de developpement ’) is not quite 
peripheral, and that in L . dichotomum. at any rate, the bundle 
attains a bilateral symmetry at the base of the petiole by the 
disappearance of the lateral protoxylems. 
There are three fair-sized bays of phloem, and the proto- 
phloem is continuous. The pericycle is from one to two cells 
thick, being one cell thick opposite the protoxylem-groups, 
and separated from them by parenchyma. 
The petiole or rachis of Z. lanceolatum , Desv., is of the usual 
type, except that it contains a large number of fibres chiefly 
in the neighbourhood of the protoxylem-groups. They are 
strongly lignified, and almost certainly produced by sclerosis 
of sieve- tubes. In addition, some of the large meta-phloem 
sieve-tubes situated in the bays of the xylem become 
lignified in different degrees. The chains of parenchyma- 
cells in the xylem have the walls separating them from one 
another considerably thickened and lignified. In the petiole 
of Z. heterodoxum , Kze., the xylem-parenchyma also tends 
to be thick- walled, and fibrous sieve-tubes are present, 
but are. not lignified. In Z. volubile , while the petiole is 
typical, the rachis shows a structure approaching that of 
Z. palmatum. 
B b 
