C. A. BARBER. 35 
right into the woody cylinder without any division into lobes. 
In monocotyledons like Asparagus the sucker proceeds thus as far 
as the sheath of the woody cylinder and undergoes no further 
differentiation, actual entry into the woody cylinder not having 
been observed (Plate VII, fig. 1). In Azma tetracantha the 
rule is that the sucker, after passing through the soft cortex, 
passes down one or more of the broad medullary rays in tongue- 
like branches. Such cases are rare and are obviously determined 
by the structure of root attacked. In ordinary dicotyledons 
with a fairly solid central cylinder the sucker, on reaching it, 
divides into two broad lobes, one on each side, which follow the 
cambial line, destroying it as they proceed. 
The following variations may be noted. In a few species 
the sucker lobes, before reaching the woody cylinder, have strayed 
tangentially in the cortex. Such cases appear to be common in 
Acacia arabica, Casuarina equisetifolia, Streblus asper, and have 
been noted in one or two other species. In most of these, how- 
ever, the sucker has ultimately reached the cambium by one or 
both lobes or by a new development of the tissue in the middle 
of the sucker. Where a sucker lobe has thus wandered in the 
cortex, the cells become after a while clear and moribund, like 
those of haustoria in contact with the woody cylinder. <A very 
distinct palisade-like tissue is thus sometimes developed and this 
is especially well seen in sections of haustoria attacking Casua- 
rina equisetifolia (Plate VII, fig. 3). One-sided entry, largely 
connected with this wandering in the cortex, is rare, indicating 
great regularity in the penetration of ordinary dicotyledonous 
roots, and the form figured (Plates VIII, IX and X) is by far 
the commonest and hardly deviated from. In the same way the 
woody cylinder is rarely entered. Azma tetracantha is an 
exception and is apparently always pierced along the broad 
medullary rays till the woody cylinder is divided up into sections. 
This species, with the soft Boerhaava repens are practically the 
only cases noted. 
The wings of the cortex of the host are occasionally 
attacked and destroyed. These wings are then in most cases cut 
