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



Neither Celtis occidentalis L. nor any of the known insects 

 forming galls on it, are reported from Europe. Houard ([11], 

 Vol. I, p. 367) mentions two mite and two aphid galls occurring 

 on Celtis australis L. and one aphid gall on C. cretica L. 



Most of the gall material and the pieces of the normal leaf 

 and petiole were collected in the latter part of the summer 

 to insure maturity, and were satisfactorily embedded in paraffine 

 and aniline safranin and gentian violet were used in staining 

 the serial sections. The one year old stem material was taken 

 in mid- winter. The studies of the witches-broom, the psyllid 

 stem galls, the lepidopterous stem gall and the structure of the 

 normal stem were made from sliding microtome sections of 

 alcohol hardened material. These were treated with iodine 

 and mounted in glycerine, a method used by Brown and shown 

 by him (not yet published) to give greater satisfaction in the 

 case of woody structures, than the longer methods of embedding 

 and staining. All drawings, histological in character, were 

 made with the aid of a camera lucida or projection lantern. 



About one-third of the work was done while the writer was on 

 the teaching staff of the Botanical Department of the Kansas 

 State Agricultural College, and he desires to express his apprecia- 

 tion of the kindly interest in the work on the part of Prof. H. F. 

 Roberts and the other members of that department. 



The remaining two-thirds of the work was completed in the 

 Botanical Department of the Ohio State University under the 

 direction of Prof. J. H. Schaffner, to whom the writer is indebted 

 for many helpful suggestions, particularly in regard to the 

 theoretical aspect of the subject. 



It gives the author especial pleasure to acknowledge the 

 very valuable assistance rendered by Mr. Forest B. H. Brown, 

 of the Ohio State University botanical staff. His excellent 

 grasp of plant anatomy has made possible a source of informa- 

 tion and inspiration, upon which the writer has drawn heavily. 



To Prof. Herbert Osborn, of the Ohio State University is 

 due the hearty thanks of the writer for the loan of entomological 

 literature. 



Much work has been done on gall anatomy in Europe, but 

 little as yet in America. The great majority of all the anatom- 

 ical papers heretofore published have been general in character, 

 dealing with many kinds of galls on many kinds of plants. 



