PHYSIOLOGIC SPECIES 
The mutations that will always attract first attention in- 
volve such morphologic structures as we have considered in 
the previous section. On the other hand, there are three 
groups of physiologic characters in the genus Cynips which 
allow additional insight into the nature of species. These 
physiologic qualities are to be observed in the form of the 
gall, the life histories, and the host relations of these gall 
wasps. 
The galls produced by the Cynipidae are, of course, plant 
tissue, but their form and structure depend largely upon the 
nature of the gall-producing stimulus which the insect puts 
into the plant. The precise source and nature of this stimu- 
lus is not known, but there seems every reason for believing 
that it partakes of the nature of an enzyme or hormone pro- 
duced by some particular insect structure. To a limited ex- 
tent the form of the gall does depend upon the plant tissue 
involved, for the possible transformations, as we have already 
pointed out (Kinsey 1923:21), are more restricted in certain 
tissues ; but beyond that the form of the gall is dependent upon 
the species of the insect rather than upon the species of the 
plant. There must be nearly as many different kinds of gall- 
producing enzymes as there are species of gall wasps. When 
a single species of gall maker attacks more than one species 
of oak, the form of the gall is essentially the same on all of 
the hosts. This point has been so often established (e.g. Cook 
1902, Kinsey 1920 :365) that it is hardly necessary to accumu- 
late more evidence. Nevertheless, the several cases in Cynips 
may be cited. 
Multiple Hosts of Cynips 
C. maculosa tritior 
C. echinus douglasii 
C. echinus dumosae 
on Q. dumosa, Q. durata 
on Q. lobata (and Q. Douglasii ?) 
on Q. dumosa, Q. turbinella 
on Q. dumosa, Q. durata 
on Q. dumosa, Q. durata 
on Q. arizonica, Q. oblongi folia, Q. Tourney i 
on Q. macrocarpa, Q. bicolor 
on Q. alba, Q. macrocarpa, Q. Michauxii 
on Q. lyrata, Q. Muhlenbergii, Q. Michauxii 
on Q. alba, Q. Michauxii 
C. echinus schulthessae 
C. teres hildebrandae 
C. plumbea 
C. fulvicollis vorisi 
C. fulvicollis major 
C. fulvicollis gigas 
C. fulvicollis fulvicollis 
( 37 ) 
