May, 1903.J Galls and Insects Producing Them. 4-9" 



a development of trichomes, especially the former. In all galls 

 the mesophj'll is subject "to 'me greatest modification. Many 

 small fibro vascular bundles are formed in this modified me.sophyll. 



3. The Acarin may be considered the lowest group of galls, 

 the Aphidid the next higher, the Cecidomyia galls the next 

 higher, and the Cynipidous galls the highest. However, many 

 of the Cecidomyia galls are lower than the Aphidid galls. 



4. The galls of Acarina and Aphididae show the greatest 

 resemblance. In these cases the method of attack is very similar 

 and is first directed against the epidermal or adjacent layer of cells. 



5. In some of the Cecidomyia galls (e. g. C. verrucola) the 

 larva appears to make its entrance into the mesoph^dl before there 

 is any pronounced modification of the cell structure. However, 

 the Cecidomyia galls are too varied and the study too incomplete 

 to make a positive conclusion. 



6. Both Adler and Fockeu consider that after the first stages 

 of formation, the gall becomes an independent organism growing 

 upon the host plant. This is probably true in the highly devel- 

 oped galls of Aphididae, Cecidomyia and Cynipidae, but the 

 writer is very doubtful if this is true of the less complex galls of 

 Acarina, Aphididae and Cecidomyia. 



This work was pursued during the year 1902-03, in the Biolog- 

 ical I^aboratory of DePauw University, but was under the super- 

 vision of Professor Herbert Osborn, of the Ohio State University, 

 to whom I am indebted for many valuable suggestions. I am 

 also indebted to two of my former students, Miss S. Emma Hick- 

 man and Miss Margaretta vS. Nutt, for aid in preparing slides and 

 making drawings. Drawings made b}- these two ladies are marked 

 with their initials. I also wish to express my thanks to my many 

 friends who have called my attention to, or have collected material 

 for, these investigations. 



LITERATURE. 



New literature will not be cited at this time, but a more com- 

 plete list will be given in connection with later papers upon this 

 subject. 



EXPLANATION OF PLATES. 



In making the drawings a Bausch & Lomb microscope, with 

 No. 2 ocular and ji objective, and a B. & L,. camera lucida were 

 used. The drawings are, therefore, larger than tho.se used in 

 Parts I and II, and the reduction not so great. The diagrams 

 are not made upon a definite scale. Drawings 34, a, b, c ; 35, a,, 

 b; 37. 38. 55, a, b ; 57, a, b, c, and 58, a, b, c, were made from 

 nature, and are ver}' little smaller than the original. The num- 

 bering of the drawings is continuous with Parts I and II. 



