Boodle.—Anatomy of the Hymenophyllaceae . 457 
phloem and the endodermis ( e ) is the pericycle, which is of 
considerable thickness, usually three or four layers of cells ; 
the conjunctive parenchyma is left blank, and the metaxylem 
is distinguished by being divided in a brick-like manner ; the 
protoxylem (px) is represented by a group of dots. The 
metaxylem takes the form of an upper xylem-band (u), and 
a lower xylem-band (/). 
A drawing of the stele of the same rhizome is seen in 
Fig. 4. The phloem (ph) forms a continuous ring *, which 
is thicker on the upper side of the stele than on the lower. 
The protophloem is at the periphery of this, and is recognized 
at several points by its small, often flattened elements. The 
phloem varies in different places from one to five elements in 
thickness. It consists largely of sieve-tubes, or elements resem¬ 
bling sieve-tubes. Their walls are rather thick and stain deeply 
with haematoxylin. In longitudinal section these elements are 
seen to be much elongated, with no evident contents, and with 
abundant pits on their longitudinal walls. From these characters, 
and from their arrangement and time of differentiation in the 
stele, there seems little doubt that they have the function of sieve- 
tubes, though unfortunately the presence of perforations and 
of callus has not so far been determined 1 2 . Though of smaller 
size, these elements in general characters resemble the sieve- 
tubes of the root of Ophioglossum vulgatum , in which Poirault 3 
describes true sieve-structure. Some parenchymatous cells 
occur here and there among the sieve-tubes, and they have 
thin walls where they abut on one another, but they have 
not been distinguished by that character in the drawing. 
Conjunctive parenchyma, one or more cells in thickness, 
separates the phloem from the xylem. The metaxylem 
consists of two bands of tracheides. Of these the upper (n) 
is more massive, and contains larger tracheides than the 
1 It is interrupted in the neighbourhood of roots. 
2 In the description of the leaf, Prantl (l.c., p. 17) states that sieve-tubes or 
similar elements could not be found in any plant in the whole order. 
3 Poirault, Recherches sur les Cryp. Vase., Ann. des Sci, Nat., 7 e ser., t. xviii, 
1893, p. 140. 
