30 
TRANSACTIONS OF THE [ Sess. LXXTII. 
(a) The pith, whose cells are, as a rule, wholly lignified, 
(b) In 
peripherally at least, was scarcely abnormal. The 
thickening! was hardly so pronounced as usual. 
Its outline might be distorted. It has, however, 
never been observed to be invaded by the parasite. 
the Bromeliaceze the vasa of the main roots are 
symmetrically ranged about the pith. Heterodera 
often occurs in the vasa where these are large, as 
e.g., in Pitcairnia spp. In some instances the 
parasites, dissected out from this position, were 
found to have attached themselves to the wall 
next the pith. 
Where the worm is established the walls of the 
vas and those of the neighbouring wood par- 
enchyma remain thin (Plate IV. fig. 5). Some- 
times they are found broken down—thus preparing 
the way for the condition first described. 
{c) The phloem seems seldom to be invaded. But in 
the vicinity of an attack it may share in the 
hypertrophy induced (Plate IV. fig. 2, ph.). 
(d) The protoxylem may afford the parasite lodging and 
be obliterated. But even if the attack be only 
near a patch of protoxylem there may be marked 
increase in the size and number of the elements, 
e.g. a Species with normally three small vessels has 
shown as many as seven or eight (Plate IV. fig. 3). 
(e) Generally Heterodera is found lying in a gall (Plate 
V. figs. 2, 3), whose long axis is roughly m a 
plane at right angles to the long axis of the 
root. Occasionally it may be placed otherwise— 
even parallel to the root axis. The gall itself is 
apparently formed from the innermost layer of 
the inner cortex, the endoderm, and the pericycle. 
Its walls consist of one or two layers of com- 
pressed cells which have been flattened against 
one another by the growth of the parasite. 
Of the creature as found little can be said. Only the $ 
has been noted. Doubtless the 7 and larve will be found 
when searched for in the soil. The $9 occur commonly 
:, In one instance, however (Pl. IV., fig. 4), the pith consisted almost 
entirely of parenchyma. 
