500 
May brook. — On the Haustoria of 
for fifteen to twenty minutes. By this method the walls of the xylem 
elements become clearly differentiated red, whilst dense protoplasmic 
contents of the parenchymatous cells of the roots, and the phloeotracheides, 
to be subsequently described in the haustoria, take up the blue stain ; the 
nucleus stains deeply with the blue stain, but the nucleolus takes up the red 
stain, and appears as a bright red spot in the nucleus. 
General Morphology of the Roots and Haustoria of 
Pedicularis vulgaris. 
As du Sablon has not described the haustoria in any great detail, for 
the sake of simplicity a general account of their morphology and structure 
will be given, followed by a more detailed account of the histological nature 
of the conducting elements in the haustoria. 
The material consisted of some roots of Pedicularis vulgaris preying on 
roots of Calluna and on its own foots. A typical root was from 4 to 6 cm. 
in length ; at the upper extremity, adjacent to the stem, it was about 3 mm. 
A 
C 
Fig. 1. A. Drawing of secondary root of Pedicularis vulgaris, bearing tertiary roots with 
haustoria. x 4. B. Portion of secondary root showing two-lipped appearance of haustoria. x 4. 
C. Drawing showing host root entirely embedded in tissue of haustorium. x 4. s.r. = secondary 
root of Pedicularis ; /.r. = tertiary root of Pedicularis ; h. and h'. — haustoria ; y.h. = young 
haustorium ; h.r. — host root ; f.r . = fine rootlet. 
in diameter, and tapered to a fine point at the penetrating end. The root 
was irregular in growth and in the method of branching ; at the upper end 
adjoining the stem signs of shrinkage were distinctly obvious on the number 
of rings present. The haustoria were borne almost entirely on the finer 
rootlets, although signs of withered haustoria could be detected on the 
secondary rootlets, and even rarely on the primary root. This points to the 
parasitic habit being adopted even in the very young stages of the root’s 
growth, although the life of these haustoria developed on the main roots is 
probably of short duration, since they die down and cease to be functional 
