A CONSIDERATION OF CERTAIN PATHOLOGIC CONDITIONS 
IN AMBROSIA TRIFIDA 
Alban Stewart 
In two former publications (8, 9) the writer has shown certain similarities 
between the structure of gall and that of traumatic tissue. In one of these 
articles the structure of an insect gall was described and figured; in the 
other a fungus gall was given similar consideration. The structures in- 
volved in both of these galls were compared with the traumatic tissue of 
the same species of plant on which the galls occurred. Certain similarities 
in the structure of both of these galls led to some speculation as to what 
might result anatomically if the same species of plant were attacked by 
both a fungus and an animal parasite. Furthermore, what would result if 
both fungus and insect should exert their influence in a gall at the same time, 
and how would the changes caused by these different stimuli compare with 
the traumatic tissue of the plant on which the gall occurred? 
I have been fortunate enough to secure material which illustrates the 
effects of these different combinations of stimuli. The stems of the great 
ragweed, Ambrosia trifida L., are sometimes infected by Protomyces andinus 
Lagh., causing large galls. The stems of the same plant are parasitized by 
Papaipema nitela Gn., which causes more or less pronounced swellings on 
the stem. Furthermore, it is quite often the case that both of these or- 
ganisms are present in the same gall, and that both have evidently exerted 
an influence on its structure. Stems which have been wounded and sub- 
sequently healed are commonly found along roadsides. A single Protomyces 
gall was also found which had been wounded. The structure of the patho- 
logic tissues arising from these various causes will be considered in this 
article. 
Gall of Protomyces andinus on Ambrosia trifida 
In a neglected spot near the railroad track at Blue Mounds, Wisconsin, 
there is a thicket of Ambrosia trifida which is badly infected with Protomyces 
andinus. This is the only station in the vicinity of Madison, Wisconsin, 
where I have found such infections. However, Dr. J. J. Davis, Curator 
of the Wisconsin University Herbarium, tells me that he has' found them 
rather commonly in other parts of the state. The galls usually occur near 
the base of the stem just above the ground, and are roughened knot-like, 
or more or less fusiform swellings, which may involve the entire circum- 
ference or only a sector of the stem. In addition to the galls which occur 
near the ground still other galls may occur higher up on the stem, in some 
instances two feet or more above the ground. Galls in these various situa- 
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