280 The Ohio Journal of Science [Vol. XVI, No. 7, 



In way of summary it can be stated that the hackberry 

 itonid galls exhibit in an especially strong fashion, specificity, 

 based upon the generic " umwallungen " type of cecidium. 

 This specificity is directly related to the specific physiological 

 phenomena of the larva and holds, whether the gall appears 

 on the young tissues of the leaf, petiole, stem or fruit. The 

 insects commonly, however, tend to oviposit on a particular 

 plant part, (this probably being the most important factor 

 in determining the position the larva eventually takes), and 

 the galls thus become associated with that part. But as in the 

 case of 16, it is seen that the character of the gall's position on 

 the plant would be of no taxonomic value whatever, since these 

 galls have developed from the young tissue of leaf, petiole, 

 stem and fruit. Many of the others have been reported from 

 more than one plant part. 



The comparison of the two generic types of prosoplasmatic 

 galls will yield some interesting data. 



Of the psyllid galls Pachypsylla mamma (6) shows best the 

 generic type to which it belongs. Occurring on the leaf it 

 can be contrasted to advantage with the numerous itonid 

 leaf galls. Given the P. mamma larva and an itonid larva (one 

 like Nos. 9 or 1,3, which commonly form galls on the upper 

 side) on the same young leaf, on the upper side there will occur 

 an entirely different series of changes as evidenced in the final 

 stages, the mature galls. In the case of the psyllid the minute 

 "cover" cone which grows up around the larva, remains small, 

 the gall being composed almost wholly of hyperplasia tissue 

 beneath and to the sides of the larva. The larva is lowered, as 

 it were, in a downward evagination, the sides of which growing 

 inward above eventually developing a thick wall over the 

 larva. The primal "cover" cone does not contribute to this, 

 but remains small and can always be seen in the center of the 

 upper concave side of the gall as a minute papilla. 



In the itonid gall very little hyperplasia takes place beneath 

 the larva, the gall being developed from the primal "cover" 

 cone, the gall becoming an appendicular structure on the 

 upper side of the leaf, while in the psyllid it is on the under. 

 Most of the itonid larvae begin operations on the under side of 

 the leaf, resulting in the gall having that position, but this does 

 not destroy the significance of the fundamental difference 

 between the two types of galls. 



