42 
ALBAN STEWART 
remainder of the section has the fungus present in it to a greater or less 
extent. 
The structure of the portion on the lower right side is similar to that 
of galls formed entirely by the insect. There is a greater radial growth of 
the bundles, as can be seen by comparing the width of the bundles with 
that of a normal bundle from the same stem (text-figure i B). The radial 
Text-fig. i. A, Diagram of a cross section of a gall formed by Protomyces andinus 
and Papaipema nitela (X 27). B, outline of a single bundle taken from a section just 
below the gall (X 27). Description of both drawings in text. 
growth of the bundles is often more than twice normal. The inner ex- 
tremities of the bundles have been eaten away in all but two cases, on the 
right side just below X where a small part of the pith remains. The bark 
on this part of the gall is but slightly thickened, being similar in this respect 
to galls which are formed entirely by the insect. To the left and above the 
area indicated by the letters, all the tissues of the stem have come under the 
influence of the fungus to a greater or less extent. The invasion of the 
fungus has been slow in a peripheral direction, and the inner ends of several 
bundles, on each side of the area X-X, show the characteristic structure 
of the xylem of the insect gall. The structure of the outer parts of the 
bundles, on the other hand, shows abnormalities commonly found in the 
Protomyces gall, especially the greater production of parenchyma and the 
reduction in number and size of the vessels. A deep depression occurs on 
the lower left side, at Y,. caused by the suppression of one of the leaf trace 
