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



The xylem of the kataplasmas showed the presence of sub- 

 normal tracheae, while that of the prosoplasmas, even though 

 occurring on vessel bearing parts, always possessed narrow, 

 elongate, spirally thickened tracheids only. 



All of the galls when compared with normal parts show 

 partial or total suppression of normal tissue characters and the 

 substitution of new characters. The new characters, no matter 

 whether little or greatly divergent from the normal, are 

 specifically related to the arthropod concerned in calling them 

 forth. 



In all of the galls, except the lepidopterous one (2), lignifica- 

 tion of certain parenchyma elements has taken place, giving 

 rise to more or less definite sclerenchyma tissue forms (pro- 

 tective layers), which in no case finds a counterpart in the 

 normal plant. This layer doubtless is definitely functional in 

 preventing mechanical injury to the larva. 



General Considerations. 



This paper does not deal directly with the etiological 

 problem, the greatest problem in cecidology, but does deal with 

 it indirectly in attempting to make clearly evident, the phe- 

 nomena appearing at the end of certain gall ontogenies; the 

 phenomena to be explained (it is hoped) through etiological 

 investigations. At this point it might be well to state (for 

 it is a fact not generally known) that the nature of the stimulus 

 applied by the insect is not known. Magnus (20), whose recent 

 work presents an excellent summary of the etiological problem, 

 closes with this sentence: " Der hypothesen sind genug 

 gewechselt, lasst uns auch endlich Tatsachen sehen." All 

 the evidence arising out of experimental studies of the problem 

 point toward a chemical interpretation (enzymes, etc., secreted 

 by the larva), but as Kiister (17) repeatedly has pointed out, 

 the experimental evidence definitely supporting any chemical 

 interpretation does not yet exist. In the true scientific spirit 

 he acknowledges the chemical theory to be, as yet, a necessary 

 inference only. 



From the preceding comparative studies, particularly those 

 of the prosoplasmas, it is clearly evident that the gall rep- 

 resents something new as far as the form content of the tissues 

 and their particular orientation is concerned. The particular 

 combination of sclerenchyma form, parenchyma form, and 



