Pedicularis vulgaris , Tournef. 
501 
with the production of the secondary and tertiary roots. Fig. r, A, shows 
a secondary root s.r. of Pedicularis, which bears tertiary roots, t.r ., on 
which are borne the haustoria h. and Ji . Fig. 1, B, shows a portion of 
a secondary rootlet bearing haustoria which have ceased to function. 
The haustoria are scattered irregularly on the roots bearing them (see 
Fig. i, a), and have no definite order of development. They are first obvious 
as small hemispherical swellings on the rootlet (Fig. 1, a, y.h). These 
increase in size and attach themselves to the host root in such a manner that 
the host root is always perpendicular to the portion of the parasitic root 
bearing the haustorium (see Fig. 1, A and c). The tissue of the haustorium 
grows up and partially encloses the host root ; thus a groove is formed in the 
haustorium which is parallel to the host root and therefore perpendicular to 
the axis of the parasitic root at 
this point. In Fig. 1, A and B, Ji ., 
the groove is distinctly visible 
owing to the host root being no 
longer attached — it has probably 
degenerated or become torn away 
— whilst in Fig. 1, A and C, h ., the 
haustoria are shown in connexion 
with the host roots h.r, The 
growth of the haustorium may 
sometimes be so vigorous that the 
host root becomes entirely en- 
closed in its tissues (see Fig. i, c). 
The haustorium depicted here is 
borne on a tertiary root t.r., and is 
also interesting in that it arises at 
the place of origin of a finer 
rootlet f.r . 
Anatomically the roots of 
Pedicidaris differ in two important details from the roots of normal 
Dicotyledons, namely in the complete absence of phloem and in the 
peculiar nature of the xylem elements. The xylem of the roots, both 
main and lateral, is composed entirely of tracheides and elongated 
parenchymatous cells, the latter being present in great abundance. The 
protoxylem consists of smaller tracheides, both spirally and annularly 
thickened. The other tracheides are all reticulately thickened, and, even in 
the oldest roots, still possess protoplasmic contents and often a nucleus. 
Fig. 2, A, is an old tracheide from a finer rootlet, and is typical of the tracheidal 
elements of the xylem. Much lignification of the walls of the element had 
taken place, yet it still showed abundant protoplasmic contents p ., and 
a large nucleus n. The place of the phloem in a normal root is taken by 
l|p£ 
: -TU 
-fi - 
k'ZW 
£b' / 
1 — -far 
p- 
w 
t T; 
Fig. 2. a. Longitudinal section of tracheidal 
element of xylem of Pedicularis , showing proto- 
plasmic contents and a nucleus, x 472. B. Longi- 
tudinal section of elongated parenchymatous elements 
which function as phloem, x 472. tr. = tracheide; 
pa. — elongated parenchymatous element ; p. = pro- 
toplasmic contents ; n. = nucleus. 
