424 
The Ohio Naturalist. 
[Vol. Ill, No. 7 , 
of the cells by the parasite. Since the parasite continues its 
attack upon different cells and the plant makes the repeated effort 
to heal the wound, we have the very active production of cells. 
The parasite making its attack upon one side of the leaf, causes 
the unequal growth resulting in a cavity. The increase in size 
of the gall causes a different tension upon the inner and outer 
surfaces and results in the elongation of cells near the outer sur- 
face as described in Part I. 
When the galls first appear they are single, but in a very short 
time others are formed just outside the first, thus forming a 
cluster. 
In Erineum anomalum (Figs. 47, 48, a, b), occurring on leaves 
and petioles of walnut, we find a condition similar to that of the 
Phytoptus galls except that the parasite is on a free surface 
instead of in a partly closed cavity. I was able to secure a very 
complete series of this gall. The first indication of the gall on the 
petiole or rib of a leaf is the increase in the amount of parenchyma 
tissue between the epidermis and fibro-vascular bundles. The 
physiological character of this tissue is also changed to some 
degree, since the cells are not so easily stained with haematoxylin, 
have rather thick walls, and contain a considerable quantity of 
tannin. The epidermal cells now begin to form tricliomes (Fig. 
47). The parenchyma tissue and tricliomes both increase in quan- 
tity, the walls of the cells become thinner (Fig. 48, a, b), and the 
deeper parenchyma tissue gradually loses its tannin, while the 
outer cells retain it in great quantities. 
These galls always occur over a fibro-vascular bundle and are 
apparently closely associated with them. These bundles become 
modified to some extent. 
The origin and development of these galls is the same as in the 
Phytoptus galls except that the parasite works upon the exposed 
surface instead of in a cavity. The fact that one produces a 
cavity lined w'ith tricliomes while the other produces a protuber- 
ance covered with tricliomes, is probably due to the fact that the 
latter is so closely associated with the fibro-vascular bundle which 
prevents the curvature but causes the rapidly-formed cells to 
swell outward into a protuberance. 
2. GALLS OF THE APHIDIDAE. 
In the Aphididae galls we have a condition very similar to that 
just described for the Acarina galls except that the shape of the 
galls are far more definite and they show a higher degree of 
development. Tricliomes are not so numerous and masses of cells 
projecting into the larval chamber as described for Phytoptus 
galls are very rare. I11 the youngest galls the cell structure of 
the leaf is modified, resulting in the formation of a large number 
of small, irregular cells, the same as in the Acarina galls. As the 
