40 
Indiana University Studies 
attested by their identical hosts and adjacent ranges (fig. 31 ), as well 
as by their morphologic identities, and heldae seems to be a species de- 
rived by physiologic mutation from conspicua stock. 
The phylogenetically ancient standing of the gall characters 
of these cynipids is evidenced in the internal structures of the 
deformations. The agamic galls of all of the species of the 
genus are produced on the veins of the leaves of white oak, 
with the single exception of Cynips heldae , which occurs either 
on leaf veins, petioles, or young stems of the oak. In most 
instances the galls appear on the under sides of the leaves. 
Beyerinck’s figures of Cynips folii (re-drawn in our figs. 113- 
117) show the order of transformation of the normal fibro- 
vascular tissue, and indicate something as to the plant ele- 
ments involved. Other European students of gall histology 
have included species of Cynips in their investigations. There 
is the work of Lacaze-Duthiers (1850-1853), Fockeu (1889), 
Hieronymous (1890) , Ktister (1900, 1911) and Weidel (1911). 
Following the suggestion of Lacaze-Duthiers, all these work- 
ers have found four fundamental zones of tissue in most cyni- 
pid galls. These zones have been called the nutritive, pro- 
tective, parenchyma, and epidermal layers, and in the degree 
and character of the development of each of these the Euro- 
pean students have seen an essential uniformity of structure 
among the European species of Cynips. 
Unfortunately, most of these histologic studies were made 
on three common European Cynips: folii , longiventris , and 
divisa. Only Weidel (1911) has given us a discerning study 
of Cynips disticha (fig. 123), and there he recognized five 
layers of tissue instead of the traditional four. My own 
studies of the gross anatomy of the galls of the entire genus 
Cynips, summarized in figures 117 to 124, lead me to believe 
that Weidel’s five layers are the correct basis of homology in 
this genus. 
If it is remembered that Beyerinck’s studies (figs. 113-117) 
show that these leaf galls originate in the phloem of the fibro- 
vascular bundle, from which they develop outwardly usually 
thru the lower epidermis of the leaf, the following interpreta- 
tions will seem warranted : 
1 . Nutritive layer. The innermost tissue of the gall, lining the 
larval cell. A distinct layer in young galls of many species, soon be- 
coming reduced by the feeding of the larval insect (and probably by ab- 
