721 
Anatomy of Solenostelic Ferns . 
slightly decurrent they disappear almost immediately below. 
The centre of the stele is occupied almost entirely by a large 
mass of pericyclic-tissue, the internal phloem being very much 
reduced, although it is still continuous all round. 
According to Jeffrey (loc. cit., p. 132) a reduced stele, 
which he describes as a tubular central cylinder with a paren- 
chymatous pith, but with no internal phloem or endodermis, 
is also to be found in Davallia stricta. The authority for the 
name of the plant on which he made his observations is not 
given, and I am in doubt as to which species he refers to. In 
Davallia tenuifolia , var. stricta (Hort.) the structure is exactly 
the same as in Davallia tenuifolia itself. 
The Vascular System of the Petiole. 
The Linds ay a-ty^o, of stele is found to be regularly asso- 
ciated with a single very simple vascular strand in the petiole. 
Seen in section this strand is subrotund or cordate in out- 
line, and contains a xylem-strand shaped like a A with the 
base directed towards the axis of the stem (Fig. 24). The 
protoxylem groups are distinct and endarch ; one occurs 
at the end of each arm of the A , and sometimes a third is 
also present at its apex. The arms of the xylem-strand are 
sometimes prolonged past the two lateral protoxylems, curving 
inwards towards the plane of symmetry of the petiole so as to 
form two small hooks (Fig. 25). These hooks are included in 
the phloem of the bundle, which is perfectly continuous all 
round the xylem-strand. According to Bertrand and Cor- 
naille (loc. cit., p. 99) these hooks are always to be considered 
as present in theory, although they are often so reduced as to 
be practically obsolete. Using the terminology introduced by 
these authors in their recent elaborate and exhaustive re- 
searches upon the leaf-traces of the Ferns, the trace with two 
protoxylems would be expressed as a binary chain of diver- 
gents, and that with three protoxylems as a ternary chain : the 
latter resulting from the fusion of two binary chains and the 
reduction of the median bipolar thus formed to zero. Both 
cases are considered by Bertrand and Cornaille to be derived 
