5° 6 
May brook. — On the Hans tor ia of 
in a reticulate or annular manner. Similarly the majority of the penetrating 
piliferous cells have become lignified. The blackened circle v.s. represents 
the vascular tissue of the mother root, now cut in transverse section ; the 
tracheidal plate is the cross-hatched portion t.p. and the portion marked by 
parallel straight lines represents the lignified elements of the ‘ nucleus * and 
penetrating piliferous layer, which connect the parasitic and host xylem. 
Fig. 3, D, represents half of this haustorium in detail; the tracheides/./. which 
have been differentiated from the penetrating cells of the piliferous layer are 
at one end in direct communication with the xylem elements xy of the host 
root h.r and at the other with the elements t.c. of the tracheidal connexion 
which have been differentiated from the small-celled tissue of the ‘ nucleus ’. 
These again are in direct communication with the elements t.p. of the 
tracheidal plate, and are practically indistinguishable from them, except for 
the larger size of the latter. 
Before proceeding to construct the anatomy of the mature haustorium 
from the sections cut and just described, and from other serial sections, a fuller 
description of Fig. 3, C, will be given, as this represents rather a unique case 
of attack. The section is a slightly oblique longitudinal one of a root h.r . of 
PediculariSy which is attacked in two places by haustoria, h. 1 and h. 2. 
Meanwhile it has itself produced two haustoria, h. 3 and h. 4, which are 
attacking two roots of Calluna , c. 1 and c .2 respectively. The root r. of 
Pedicularis acts as host to the two haustoria h. 1 and h. 2, and hence, since it 
is itself cut in longitudinal section, these two haustoria are cut in the plane 
of section which gives a transverse section of the mother roots at the point 
of origin of the haustoria. Again, the root h.r. acts as the mother root of the 
two haustoria h. 3 and h. 4, whose host roots are respectively c. 1 and c. 2. 
Here, since the mother root h. r. is cut in longitudinal section, the two host 
roots c. 1 and c. 2 are cut in transverse section and the plane of section of the 
haustorium is the same as that shown in Fig. 3, A. Hence, here in one 
figure there are represented, typically by h. 1 and h. 3, the two planes of 
section of a haustorium, which give the two principal views of the anatomy 
just described. 
From Fig. 3, A and c, h. 1, it can be seen that the differentiation of 
the palisade-like elements of the piliferous layer takes place in one plane 
only, the plane of section of the haustorium represented in Fig. 3, c, h.i. 
This is also true of the cells of the ‘ nucleus * which become differentiated 
for conduction. The tracheidal plate, however, is not elongated in one 
direction, but is disc-like in shape, varying in thickness, but generally about 
three or four cells deep. Thus the mature haustorium consists of tracheidal 
elements arranged in a row, varying from one to three elements in thickness, 
and running in a direction parallel to the length of the host stem ; these are 
surrounded by an elliptically shaped mass of small-celled tissue, the ‘ nucleus 
the long axis of the ellipse being represented by the row of tracheidal 
