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



The evagination beneath the larva so prominent in the case of 

 P. mamma could not, naturally be carried out on the stem, hence 

 the hyperplasia in that case is almost entirely lateral to the 

 insect and above it. Discounting the factor of the plant part 

 selected there is the quantitative evidence indicating specificity 

 in the intensity of the stimulus which developes the generic 

 type of gall. 



Compared with the normal tissues these galls show the 

 abortion or complete absence of certain normal specialized 

 cells, such as stomata, cystoliths, tracheae, bast, wood fibres 

 and sieve tubes. 



Prosoplasmas. Dipterous galls. (Itonididas). 



Galls of Cecidomyia unguicola (S) and Phytophaga celti- 

 phylla (9) were chosen to illustrate in detail the definite speci- 

 ficity which characterizes these highly evolved forms of proso- 

 plasmas, which are induced by the insect larva to grow upon the 

 same leaf. This fact of the gall species being definitely and 

 constantly related to the insect species, is a fact of far reaching 

 significance. It has long been known among European workers 

 and Cook (2) on a histological basis, first called attention to it 

 in America. 



In the case of these two galls some of the contrasting 

 characters are: Notable difference in size (they are drawn to 

 same scale). In 8 the proximal development of large celled 

 parenchyma, opposed to its distal development in 9. Much 

 thicker protective and nutritive layers in 9 than in 8; shape of 

 layers also different. Apical canal tightly closed proximally in 

 9, open throughout in 8. Trichomes in apical canal of 9 smaller 

 than those in canal of 8. Large acicular trichomes developing 

 over surface of 9, while 8 is always perfectly smooth. Hyper- 

 plasia of leaf at base of gall, extends much farther in 9 than 8. 



Comparing the other itonid galls in a similar manner will 

 yield just as striking results. In the following discussion of the 

 remainder of the galls, only the more significant specific 

 characters will be emphasized. 



Phytophaga wellsi (10) is the least specialized. Its pro- 

 tective layer merging insensibly into the distal parenchyma and 

 its simple closed apical canal are the two most important 

 characters placing it below the others in the degree of complexity 

 attained. 



