May, 1916] Morphology of the Zoocecidia of Celtis 279 



No. 11 is similar to 8, but simpler. It is constantly smaller 

 and does not develope the expanded base, so characteristic of 8. 



The extension of the protective layer to the apical canal is 

 found in No. 12 only. 



In No. 13, the epidermis lining the chamber at the apical 

 end of the gall is composed of perpendicularly elongated cells 

 which are filled with a fine granular substance (Fig. 13b, at x, 

 pi. XVII), the nature of which was not determined. The char- 

 acter was constant, being exhibited in many galls examined. 

 Such a cell layer was not observed in any other itonid gall. 



No. 14 has the fibro-vascular bundles traversing its sharply 

 defined protective layer. In this respect it is similar to 9. 

 These two galls differ from all the others, having definite 

 protective layers, in this character. Kiistenmacher (14) has 

 noted the diversity in Rhodites galls in this regard. 



The alate condition of 15 makes it an object instantly 

 indentifiable. With this character is associated the peculiar 

 distribution of the bundles (Fig. 15a, pi. XVII), not found in 

 any other gall. 



No. 16 possesses many characters setting it apart from the 

 others, the most important of which is the development of the 

 dehiscence layer in it, permitting the larval chamber to drop out. 

 Nothing in any of the other galls is directly comparable to it. 



All of the hackberry itonid galls are of the " umwallungen " 

 generic type. The kinds of cells found in the galls are not widely 

 dissimilar, the specific characters being confined to the kinds of 

 tissues, with particular reference to the form the tissues assume. 



There is a character which the writer desires to point out, 

 which is found not only on most of the itonid galls of the 

 hackberry, but on those of other plants, the significance of 

 which has not been determined so far as the author is aware. 

 The protective layer in most of these galls is sharply delimited 

 apically giving rise to a distal segment of the gall composed 

 wholly of parenchyma (No. 12 excepted) a segment which is 

 evident in many galls upon superficial examination. 



It is proposed to call this segment the "apical segment," 

 though the writer has not used this terminology in the present 

 paper because of the uncertainty as to its value in taxonomic 

 description. No ontogenetical studies of this type of gall 

 have as yet been made by the writer to demonstrate if this 

 apical segment bears any relation to the minute cone which 

 early developes over the newly hatched larva. 



