507 
Pedicular is vulgaris , Tournef. 
elements. The cells of the ‘ nucleus ’, and also the row of tracheidal elements, 
are in direct communication with the cells of the tracheidal plate, which is 
adjacent to the vascular tissue of the parasite, and all food material drawn 
from the host has to pass through this disc on its way to the parasitic root. 
The whole of this central tissue of the haustorium is surrounded by a cortex, 
which in most places is from four to six cells deep. 
One of the haustoria examined exhibited a peculiar arrangement of the 
conducting tissue, which was interesting in so far as it showed a modification 
in the direction of economy of conduction elements. A median longitudinal 
section, of a haustorium of Pedicularis had been cut in the plane giving 
a transverse section of the host root, hence the type of section illustrated in 
Fig. 3, A, was shown. One of the 
cells, Fig. 4, /.A, of the piliferous 
layer, adjacent to a xylem element 
of the host root, had become thick- 
ened in the usual way, and still re- 
tained its contents. The cell t.c. 1 of 
the conducting tracheidal strand 
which was adjacent to this element 
p.t. was elongated to an abnormal 
extent, and in a direction perpen- 
dicular to that of the axis of the 
haustorium, and therefore perpen- 
dicular to the normal direction of 
elongation of these elements. The 
remaining elements of the tracheidal 
strand were of the normal form. 
The solution absorbed by the ele- 
ment p.t. from the host xylem ele- 
ment xy passes into the element 
t.c . 1, whence it can be passed into each one of the cells n.c. y and also the 
cell t.c. 2. Hence this phenomenon would appear to be a unique effort 
on the part of the haustorium towards economy of conducting material. 
It has already been mentioned that the parasitic root preys on other 
roots of the same or a different plant of Pedicularis. When such was the 
case no difference in the structure of the haustorium arose. Barber 1 has 
shown that where Olax attacks itself marked differences occur in the 
structure of the haustoria ; all the vascular tissues of the mother root are 
continued down the entire length of the haustorium, and at the penetrating 
end enter into connexion with similar elements of the host root, the 
connexion being of the nature of a fusion. No such difference was found to 
exist in haustoria of Pedicularis in cases of self-attack, but the method of 
1 Barber, C. A. : Mem. Dep. Ag. Ind., Lot. Ser., vol. ii, 1907. 
M m 
Fig. 4. Detailed drawings of a few cells at 
the penetrating end of a Pedicularis haustorium 
showing unique arrangement of haustorial 
tracheidal element t.c. i. x 326^. xy. = host 
xylem element ; p.t. = cell of piliferous layer 
tracheidally thickened ; t.c. 1, t.c. 2 = cells of 
tracheidal connecting strand ; n.c. = cells of 
‘nucleus’ adjacent to elongated element t.c. 1. 
The arrow denotes the direction of the longi- 
tudinal axis of the haustorium. 
