528 Philippine Journal of Science 1919 
a physician to Innocent XII, and professor of medicine at Bo- 
logna and, later, at Messina. In his De Gallis, which is the ear- 
liest systematic treatise on galls, he maintained that, at least in 
the case of Cynips, the galls formed on the plant were caused 
by a certain acid secreted by the insects. A more recent paper 
by A. Cosens has the following to say in connection with these 
chemical secretions: ° 
The larva secretes an enzyme capable of changing starch to sugar 
[and] which acts on the starchy constituents of the nutritive zone [of 
the gall] and accelerates the rate of their change to sugar. The material 
thus prepared supplies nourishment to both the larva and the gall. 
Galls can be produced only “when the tissue of the plant is 
interfered with during, or prior to, the actual development of 
the tissue.”° After the plant tissue has become fully matured, 
no amount of stimulus, whether physical or chemical, will lead 
to the formation of galls. 
In the present work only galls caused by the action of animals, 
known as zodcecidia, are taken into consideration. A zodceci- 
dium may be caused by the action of a member of either of two 
zodlogical classes—Insecta and Arachnida. Galls caused by the 
former vary in structure from a simple convolution in the leaf 
lamina or a swelling in the stem to a more or less complex for- 
mation on different parts of the plant. Insects that have the 
power of producing plant galls are confined to the sacagiaes or- 
ders and families: 
Order. Families. 
1. Rhynchota, or Hemiptera. Psyllide, Aphidide, and Coccide. 
2. Diptera. Itonidide, or Cecidomyiide, and 
Trypetide. 
3. Hymenoptera. Cynipide and Tenthredinide. 
4. Lepidoptera. Gelechidex. 
5. Coleoptera. Buprestide.” 
6. Thysanoptera. 
Arachnid gall-makers are all mites, which are members of the 
family Eriophyide (formerly called Phytoptide). Galls caused 
by this family are called erinea* and are generally simple con- 
volutions in the leaf famina, with hairy outgrowth on the 
concave surfaces. When the gall is young, the gall-making 
eriophyids are found among these hair tufts. 
“Cook, M. T., op. cit. 802. 
* Trans. Canad, Inst. 9 (1912) 297-387; [Ent. News 24 (1913) 187-189.] 
‘Butler, F. H., Galls. Encyel. Brit. 11 (1910) 425. 
"Cook, M. T., op. cit. 802. 
. Banks, Nathan, Acarina or Mites, Rep. U. S. Dept. Agr. 108 (1915) 135. 
