36 STUDIES IN ROOT-PARASITISM. 
off by the formation of cork below the injured places. Corky 
layers surrounding the wings appear with great frequency, thus 
protecting them from further injury. Cork is also found as with 
Santalum in a number of cases in the tissues opposite to the 
ends of the sucker lobes. 
Secondary thickening in the root attacked is far more general 
than in the attacks of Santalum, and the cortical wings ina 
great number of cases join in this secondary wood formation. 
Such wood, formed after the attack has reached the cambium, 
deviates at first from the normal, having thinner elements, less 
sclerotic cells and fewer vessels in the wood (cf. Santalum, Part II, 
para. 19, Note). The formation of gum or thyloses in the 
cavities of the vessels opposite the cells of the sucker occurs as 
under the attacks of Santalwm haustoria, and in many cases this 
formation is markedly confined to the region between the ends of 
the lobes of the sucker. 
On the whole, the haustoria of Olax scandens rarely fail to 
enter a root attacked, possibly thanks to the complicated and 
long-lived gland. Moribund haustoria have been much more 
rarely met with than in Santalum, but the tracts of country from 
which the collections were made were very different and no 
definite conclusion can be drawn from this. The test for full 
activity or waning power is the relative absence of contents in 
the cells. In Olax it is chiefly the older haustoria which are 
thus emptied, such as have developed secondary thickening. The 
entry, as we have seen, is regular and usually along the cambial 
line. But when this has been effected, the haustorium does not 
appear to be so destructive of the host’s tissues as that of 
Santalum, whether in the wings or in the woody cylinder. 
The action of the sucker cells upon the tissues of the host 
opposite to them seems to be similar to that noted in Santalum. 
In places, the influence can be seen at a distance by the formation 
of new bands of sclerenchyma or cork opposite the point of 
attack, the formation of gum or thyloses in the vessels or 
the yellowing of bands of sclerotic fibre in the cortex. But 
there is no clearing of starch in the host’s root opposite the 
