6 jo Benson.—Root Parasitism in Exocarpus. 
H, cut longitudinally in the median plane. The drawing is constructed 
from a series of sections stained with safranin and aniline blue. F is the 
foreign root upon which the haustorium is preying. The neck, N f of the 
haustorium contains reticulately thickened tracheides. These are continuous 
with the conducting cells of the ‘ nucleus ’ of the haustorium. The nucleus 
is composed of two parts : the central core, C, of nucleated transparent cells, 
and the vascular sheath, V, which covers the whole surface of the nucleus 
and is often many cells thick, especially on the proximal surface, where it 
Text-fig. 2. An Exocarpus root in transverse section bearing a haustorium with a sucker 
which has reached to the centre of the stele of a foreign root. The cortex cells of the latter have 
been omitted for clearness. Starch grains were present in all the cortical cells of the parasite, 
but have been purposely omitted except in a few cases. Further description in the text, 
x 135- 
forms a kind of pad. In the distal part it is continuous with the lignihed 
collecting cells in the sucker, vS. The vascular elements of the haustorium 
I propose to refer to under the name of phloeotracheides for reasons which 
are given later. The walls of the tracheides of the neck and of the phloeo¬ 
tracheides differ from those in the xylem of the mother root in the absence 
of circular bordered pits (compare Text-figs. 3 a and 3 b). The phloeo¬ 
tracheides contain a thin layer of matrix in which are embedded small 
approximately spherical bodies which stain a bright blue with aniline. As 
