Cc. A. BARBER. 27 
The sucker cells in contact with the host’s root are similar 
to those in Santalum. Those at the ends of the lobes are 
secreting, pouring out the characteristic (yellow) mucilaginous 
substance in which the cells are seen to radiate (Plate X, fig. 2). 
After the secreting edge of the lobe has passed and connection 
has been established between the cells of haustorium and host, 
the organ becomes absorptive, and reticulated vessels are formed 
along the main lines of transport. The cells in contact with the 
host’s root are elongated and form a palisade-like layer which is 
specially distinct in old haustoria which have lost their contents 
(Plate X, fig. 1). In all these respects the resemblance between 
the suckers of Olax and Santalum is very close. 
15. It will have already been noted that the vascular tract 
in the lower part of the haustorium in Olax differs from that in 
Santalum in the absence of a pith or median parenchymatous 
tissue. There is a single, median plate of vessels in place of two 
parallel ones. The absence of this parenchyma is perhaps one of 
the chief peculiarities in Olax, as it is present in all the other 
haustoria of the series examined, and it is accompanied by 
great differences in the early stages of development of the 
haustorium. 
In Santalum the nucleus is seen to project upwards between 
the two diverging arms of the vascular loop (Plate IX, fig. 4, 
dotted line) and, in older stages, its upper limit is marked by a 
transverse collapsed layer (fig. 5). The vascular loop is open 
below and, in young stages, its two arms pass downwards into 
procambial strands on either side of the nucleus. In Olax, on 
the other hand, the vascular loop is closed below by a transverse 
plate of vessels and the nucleus is separately formed below this 
region (fig. 2). The procambial strand is formed above the gland 
in the median line and the vessels are not developed until the 
gland has been pushed down against the woody cylinder of the 
host’s root (fig. 3). 
Figure 1 on Plate VIII shows a very young stage of the 
vascular tract in Olaw haustorium, the vascular loop passing down 
