May, 1916] Morphology of the Zoocecidia of Celt is 281 



Histologically the itonid galls show a much higher condition 

 in the definiteness with which the nutritive, protective and 

 parenchyma tissues are distributed. Also, greater diversity 

 of specific characters is introduced by the larvce, in itonids 

 than in psylhds for in the latter a definite part of the form 

 character is related to the kind of plant part on which the gall 

 is developed. In the itonids the form character is wholly 

 related to the larva. 



Comparing the prosoplasmas with the normal tissues it is 

 strikingly evident that we have, as many European cecidologists 

 have pointed out, entirely new structures. This "newness," 

 however, in the hackberry prosoplasmas, consists of new forms, 

 assumed by tissues, which are composed of cells that have 

 close if not identical counterparts in the normal parts. Com- 

 monly the parenchyma and sclerenchyma elements of the gall 

 tissues are much larger than those found in the unaffected 

 structures, but in no case can it be said that the cells of the galls 

 are fundamentally different from those observable in the 

 normal plant. 



Heteroplasmas, (All of the galls). 



In comparing the kataplasmas with the prosoplasmas, it can 

 be inferred that the amount of embryonic tissue influenced in 

 the beginning stages of the gall is greater in the former than in 

 the latter. In the case of the lepidopterous gall the fact of 

 the greater range of the stimulus is doubtless associated with 

 the relatively greater size of the larva; in the mite gall, to the 

 numerous individuals present at a particular point of attack. 

 In both cases this condition is enhanced by the migration of the 

 arthropods from one part of the affected region to another, a 

 phenomenon known to take place in these galls, but which 

 is not true of the prosoplasmas. In these the larva is quiescent, 

 while the definite new form of tissue is growing about it. This 

 has been demonstrated by the writer in P. mamma and by 

 Fockeu in dipterous galls. The low type of heteroplasia 

 (kataplasma) relatively undifferentiated, and the highly differ- 

 entiated form (prosoplasma) undoubtedly owe their difference 

 in great part to the distinction in the arthropods just pointed out. 



It should be noted that the difference between kataplasmas 

 and prosoplasmas is not a difference in kind, but a difference in 

 degree only, as Kiister (15) pointed out when first presenting 

 this terminology. 



