215 
thus favoured. One may suppose, to express the matter 
differently, that the burr- or bird’s-eye-type of structure, 
while making longitudinal conduction more difficult, will scarcely 
reduce facilities for conduction in a radial direction, i.e., towards 
the cambium. Hence one may regard the supply of nutriment 
to this tissue as being rendered relatively somewhat easier than 
in normal wood and bast. A similar suggestion may be made 
with regard to ordinary burrs on the stems of various trees, 
namely, that one of the factors concerned in the progressive 
enlargement of the burr may be the special structure of the 
wood and bast* as affecting conduction. Other factors may 
be more directly connected with the presence of numerous 
arrested adventitious buds or roots. 
The four specimens from Hampton Court show some diseased 
wood continuous with the remains of dead branches, decay 
aving gone so far in the large specimen that a central cavity 
(inhabited by wood-lice) extended through part of the swelling. 
A little diseased wood also immediately surrounds many 0 
the dead sinkers individually, or forms a confluent patch where 
they are crowded. The occurrence of diseased wood, other 
than that in the mistletoe-cankers, appears to have played no 
part in the origin of the swellings, but, when an enlargement has 
been formed, decay of a considerable tract of the inner wood 
might favour more rapid enlargement by causing the flow of 
sap to be confined to the outer wood, 7.e., the region of the wood 
showing more or less burr-like structure owing to the action 
of the mistletoe. Possibly most of the large swellings on the 
Lime may have a hollow centre, but data are not available 
on this point. 
Elwes}, when referring to the occurrence of burr-like 
swellings and of mistletoe on branches of Lime-trees in Essex, 
stated that ‘no mistletoe was now present on many of the 
branches so malformed,” but expressed the opinion that the 
occurrence of the swellings “might be wholly or partially due 
to the arrested growth of the branch where the mistletoe had 
taken root on it.” Possibly the branches described as bearing 
no mistletoe may have been viewed at a little distance, in 
which case diminutive sprouts of mistletoe might have been 
overlooked. Perhaps, on the other hand, the aerial shoots 
of the parasite may completely disappear in some cases. 
eS ee 
* Enlarged medullary rays form a frequent character of these burrs 
as well as the contorted grain. 
+ Elwes, Gard. Chron., ser. 3, vol. 41 (1907), p. 224. 
