26 STUDIES IN ROOT-PARASITISM. 
portions coalesce and form the ordinary collapsed layers of the 
mature haustorium, an inward process permanently marking the 
point of junction. In such a mature haustorium the upper end 
of this collapsed layer points to the top of the nucleus or to the 
angle formed by the vascular strand of the axis and the base of 
the vascular loop. This development of the collapsed layers in 
Olax is very different from that described for the haustorium 
of Santalum. In Santalum the collapsed layers are formed 
much further out and their upper end passes well outside the 
whole vascular loop, and, in non-median sections, right round it. 
These differences are illustrated by the diagrams 2—5 on Plate IX; 
fios. 2 and 3 represent young and mature stages of the haus- 
torium of Olax, 4 and 5 of Santalum. The collapsed layers are 
indicated by the letters ¢. 1. 
The gland, which is such a marked feature in the young 
haustorium and is apparently constantly present in haustoria 
of any size, leaves no trace behind it in the ordinary mature 
haustorium, thus again contrasting greatly with the behaviour 
in Santalum. This constant absence of traces of the gland in 
older sections at first caused great surprise. It was surmised 
that its disappearance was due to the disorganized nature of 
the gland in its older condition, to the great force with which 
penetration is effected and the hardness of the woody cylinder 
of the host’s root against which it is pressed. Sections cut 
later through soft roots confirmed this view. In 12 cases dis- 
tinct traces of a former gland have been met with, and these 
are all or almostall in attacks on soft-tissued hosts, Azuma tetra- 
cuntha and Asparagus racemosus being typical examples. Every 
section cut of haustoria penetrating these roots shows traces of 
the gland (Plate VII, figs. 1 and 2). The part of the oland left 
is presumably the last remaining cells of the cap of densely 
crowded cells at the top of the active gland and possibly portions 
of the duct. The comparison of Olax and Santalum in this 
respect will be rendered clear by a reference to the diagrams 3 
and 5 on Plate 1X, where gl indicates the remains of the gland 
after penetration, 
