C. A, BARBER. 18 
young and “unopened” there may still be some difficulty in 
locating the exact line of separation between.the outer, starch- 
laden and the inner, clear tissues; the transition is as yet 
gradual. When, however, the gland is fully formed and throwing 
out its secretions, this line of separation is so striking that it 
arrests the attention at once (Plate IV, fig. 4, and Plates V and 
VI). This will be dealt with later. 
The haustorium, as yet without penetration into the host’s 
tissues, but possessed of the complicated structure shown in 
fig. 1 on Plate V, may be assumed to have reached its complete 
youthful form. As we shall see, the mere act of entering causes 
a complete change and presents us with an entirely different 
structure whose parts are difficult to recognize. The develop- 
ment having reached a certain stage, it will be well to consider 
the appearances in detail, as well as to compare the arrangement 
of the tissues with that of the haustorium of Santalum at a 
similar stage. For this latter purpose, we may refer to figure 
22 on Plate V of Part I of the description of Santaluwm haus- 
toria. A single glance at that figure is enough to show what 
great differences there are in the development of the haustoria 
in these two plants. 
The nucleus in Olaa cannot be made to agree with that 
in Santalum. In Olax there is a sharp separation between 
nucleus and vascular loop: in Santalum they are merged in one 
another and the nucleus passes some way up, projecting as a 
mass of parenchymatous cells in the median line between the two 
arms of the loop (Plate IX, figs. 2 and 4). The starch-filled cells in 
Santalum surround the nucleus closely and, further out, a distinct 
line separates them from the clearer outer cells. The reverse is 
the case in Olaz, the denser cells being outermost. Moreover, this 
line of separation between the clearer and denser cell elements 
abuts, in Santalum, on the axial region at the middle of the 
vascular loop, in Olax opposite the middle of the gland, which 
is much lower down. The sucker in Santalum is formed of 
nucleus and cortex, but in Olax only the former takes part in 
its construction. And these differences are but the prelude to 
