Cc. A. BARBER. 9 
make any impression on the root attacked. We shall proceed to 
consider the internal structure of such. 
In the earliest stages of development met with in the 
sections examined a differentiation has already occurred in the 
tissues. These are divided into an outer and an inner zone 
(Plate IIT, fig. 1). A peripheral zone of irregularly arranged, 
more or less permanent cells surrounds the whole of the rest as a 
sort of mantle. The contents of these cells have largely dis- 
appeared, there is little or no starch, and rows of calcium oxalate 
crystals have made their appearance. Not infrequentiy the cells 
are crushed in places and intercellular spaces occur here and there. 
This crushing of the tissues is most pronounced at the inner 
border of the zone where it joins the central mass, and here too 
the intercellular spaces are not infrequently united to form a 
series of lacune. 
The inner zone is at once seen to be the living, active part 
of the haustorium. The cells are small and full of contents, 
arranged in radial rows and rapidly dividing in a plane parallel 
to the surface of the host. Curves of growth are thus produced. 
In the case figured they are already commencing to bend inwards 
towards the middle line. 
At the proximal end the vascular elements of the mother 
root enter the haustorium, bringing the materials for its develop- 
ment (Plate ITI, fig. 2). Where, as in fig. 1, the section is not 
quite median, masses of smaller, darker cells indicate the place 
where the vascular loop will make its appearance and unite the 
haustorial axis with that of the mother root. These procambial 
masses are formed in the zone of radiating cells. 
There is yet another differentiation which has already made 
its appearance. The contents of the radiating cell are not 
equally distributed through the zone. The parts nearer the 
host’s root are distinctly clearer than those outside them and, in 
thick sections, a band of cells with darker, starchy contents may be 
traced right round near the line of separation of inner and outer 
zones. This dark area forms a sort of cap over the inner, clearer 
portion and it is presumed that it is due mainly to the greater 
