PATHOLOGIC CONDITIONS IN AMBROSIA TRIFIDA 
41 
yond where the gall occurs. That they are formed especially for food seems 
unlikely, as they contain but little substance that could be used for food. 
The great similarity between these parenchyma masses and callus tissue 
leads one to suspect that possibly the wound stimulus, resulting from the 
gnawing of the insect, might have caused them. Indeed, similar instances 
have already been reported. Kiister (3) discusses this phase of the subject 
at some length. In one instance (p. 279), he states: "Auch in ihren Ent- 
wicklungsstadien konnen die Gallen noch durch Wundreize beeinflusst 
werden. Im Innern die Potania-Gallen wird das zartwandige Parenchym, 
das die Larvenkammer auskleidet, und dessen Zellen den Fresswerkzeugen 
der Gallbewohner zum Opfer fallen, immer wieder durch callusartig Wucher- 
ungen regeneriert." There is also a possibility that the callus-like masses 
result from a stimulus the object of which is to fill the gall cavity with tissue. 
Kiister (p. 314) mentions instances of this kind in which the gall had been 
abandoned by the insect. 
In young galls, where the pith was not entirely eaten away, a ring of 
cambium-like cells was sometimes found near the border of the cavity. 
The bundles themselves are sometimes able to proliferate inward, the con- 
dition in this respect being similar to that described by Cosens from the 
gall of Eucosma scudderiana. Where conditions of this kind occur there is 
usually xylem present next the cambium ring, but a short distance inward 
the character of the cells changes and there is nothing but parenchyma. 
Sometimes the parenchyma extends to the cambium ring for a considerable 
space, having entirely replaced the xylem. Bands of cambiform cells occur 
in these parenchyma masses similar to those which occur in the callus 
growths already described. They are both eaten by the larva to some 
extent, but it seems unlikely that they are formed by the plant for this 
purpose through some stimulus from the larva. 
Gall of Protomyces andinus and Papaipema nitela on Ambrosia 
TRIFIDA 
In the thicket from which the Protomyces galls described in this article 
were taken there were also plants of Ambrosia trifida which bore galls of 
Papaipema nitela. I was fortunate enough to find several galls in which 
both fungus and insect were present, and from the structure of these it was 
evident that both organisms had contributed to their formation. In some 
of these galls the fungus was confined to a sector of the stem, as was shown 
by the presence of the sporanges in this part only. From facts already 
mentioned in this article, we can safely assume that the opposite side of 
the gall, which contained no sporanges, had not been influenced by the 
fungus in its development. A diagrammatic drawing of a cross section of 
one of these galls is shown in text-figure i. On the lower side of the figure, 
between the letters X-X, there is a sector, including about one fourth of the 
stem, which has no sporanges or other indications of the fungus in it. The 
