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



sudden transition from delicate sub-hyaline tissue to opaque 

 hard tissue. Sooner or later the tip breaks off at this point. 

 Riley states that "while issuing the perfect insect pushes off 

 the tip." This gall is the most common of all the itonid galls 

 of the hackberry; a hundred may often be found upon a single 

 leaf. 



Rilev, oth Rept. U. S. Ent. Comm. Gall No. 34, p. 614. 1890. 

 Beutenmuller, Bull. Am. Mus. Nat. Hist. 23:388, PL 13, Fig. 9. 1907. 



The entire longitudinal section of this gall is illustrated in 

 detail in PI. XVII, Fig. 8a. This figure and the next are 

 slightly diagrammatic in that the fibro-vascular bundles, which 

 traverse the gall longitudinally without branching, are shown 

 continuous, when actually they would be broken in any one 

 of the serial sections, due to the fact that they do not pass to 

 the tip of the gall in one plane. 



The epidermis is uniformly composed of simple tan- 

 gentionally flattened cells. The nutritive and protective layers 

 assume an elongate cup shape, whose base is surrounded by the 

 parenchyma tissue, which gives the gall base its flaring aspect. 

 The nutritive layer is very thin, seldom over three cells in thick- 

 ness. Note the unbroken condition of its superflcial cells. 

 The larvcB in all of the galls of this type do not feed on the cell 

 tissues, but on the food material which passes into the chamber 

 through the cell walls. The protective layer is sharply delimited 

 from the nutritive, a condition common to all of the itonid 

 galls studied. On its outer side the protective layer is only 

 sharply set apart from the parenchyma on the side toward 

 the leaf. 



The nature of the cells composing the protective layer is 

 shown in Fig. 8d, a small group of cells at the proximal end 

 of the layer. The walls contain innumerable simple narrow 

 pits, which pass to the middle lamella. This latter structure 

 is in all cases continuous between the cells. Crystal cells are 

 found in abundance directly adjoining the lignifled thick walled 

 cells, a condition obtaining in the normal stem (PI. XII, Fig. A). 

 Figs. 8e and 8f show the sclerides of the 1 yr. and 3 yr. old 

 stems respectively, and are drawn to the same scale as those 

 from the gall. The great majority of the lignifled cells of the 

 galls are largei inan any found in the stem or in the stone of 

 the fruit. 



