22 
Indiana University Studies 
It appears that wherever the gall-producing capacity is 
primitive the insect will produce little hypertrophy, the form 
of the gall will not be restricted by any very specific insect 
physiology, and the choice of tissues in which to oviposit will 
not be restricted by peculiar sensory physiologies to the extent 
found among higher Cynipidse; but on the contrary any ac- 
tively growing tissue available at the season will be utilized 
in oviposition, and the relatively small amount of hypertrophy 
will assume a form determined by the plant tissue. In all 
of these instances, the two or more forms of galls occur on 
different tissues, indicating that the nature of the tissue is 
largely responsible for the result. This is most evident from 
a study of those instances of polymorphism which ever include 
galls produced on anther tissue. In every one of these cases, 
the anther gall is a small, seed-like, egg-shaped, thin-walled, 
hollow capsule, irrespective of the forms of other galls which 
the same insect produces on other tissues. An examination 
of all the known anther galls confirms the opinion that the 
anther is capable of producing little else than this capsule, 
particularly if it is only a primitive insect which attacks 
it. These simjDle capsules are inhabited by Neuroterus duhius 
clorkex (at times), N. vermis exiguus (at times), N. floricola, 
Plagiotrichus exiguus, Andricus gig as, A. pulcher, A. 
blastophagus, and the European species A. fceeundatrix pilosus, 
A. nudus nudus, A. beyerincki, A. cerri, A. burgundus, and 
A. occultus. Clustered masses of similar capsules are found 
in Neuroterus minutus pallidus and in Andricus serricornis. 
Less similar but of essentially the same structure, are the 
galls of Andricus dubiosus. The diversity of these insects 
will be more apparent if it is remembered that the genus 
Andricus is an assemblage representing several lines of evolu- 
tion. Only a very few galls of any other form are described 
from anthers, and I have not been able to examine material 
enough to be certain that it is not the stamen stem, the 
flower bracts, or the ament stem itself which is involved in 
the apparent exceptions. 
If one should need any further proof that it is the plant 
tissue and not the insect which determines the forms of these 
galls, that proof comes from Neuroterus vernus exiguus and 
Plagiotrichus exiguus, where only two kinds of galls, an 
anther capsule and an ament stem swelling, are produced. 
