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The Ohio Naturalist. 
[Vol. II, No. 7 , 
5. The families show parallel lines of development from a low 
form of gall structure up to a high form . e. g., Aphididae and 
Cynipidae. 
6. I am inclined to believe that the modification of the plant 
tissue is purely mechanical. The loss of differentiation between 
palisade and mesophyll and the closing up of the intercellular 
spaces would be a natural result of rapid cell division. The 
elongation of cells in certain directions would be a natural result 
of mechanical tension arising from rapid growth. I11 the family 
Aphididae where the gall is primarily a folding of the leaf the 
elongation of the cells is parallel with the surface of the gall. In 
those galls where the formation is a thickening of the leaf the 
long axis of the cells is perpendicular to surface of the formation. 
7. The presence of at least two zones, of which the inner may 
be considered nutritive, is very common. 
8. The formation of the gall is probably an effort on the part 
of the plant to protect itself from an injury which is not sufficient 
to cause death. Both Adler and Fockeu consider that after the 
first stages of formation the gall becomes an independent organ- 
ism growing upon the host plant. 
9. Trichomes are far more prominent in galls produced by 
mouth parts than in those produced by oviposition. 
10. It appears from these studies that the histological charac- 
ters of the gall will prove very important in determining the 
characters of the species. 
Part II. Apical Bud Galls. 
In my third conclusion in the preceding paper I have expressed 
a belief that galls produced by the same genus of insects show a 
decided resemblance even though produced on widely different 
plants. Furthermore, this similarity seemed to be due to the par- 
ticular part of the host plant to which the stimulus was applied. 
The following study of the apical bud galls seem to indicate 
that when corresponding parts of different plants are stimulated 
by insects of different genera that the galls produced have char- 
acters in common. 
The gall produced by Cecidomyia solidciginis L,w. (Fig. 31) is 
merely a large bunch of leaves at the end of the stem of Solidago. 
The cone-shaped gall of Cecidomyia salicis-strobiloides O . S. (Fig. 32) 
at the tip of the twigs of Salix is a bunch of leaves reduced in 
size and so compactly arranged as to produce the peculiar cone 
effect. A further examination of these two galls shows that the 
tips of the stems are enlarged and that the larval chamber is in 
the apex. 
A superficial examination of the gall of Callirliytis clavula Fitch 
(Fig. 33 a. b. c. d.) shows no resemblance to the preceding galls 
except in location at the tip of the stem. The gall is apparently 
